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Define Force:
Topic 4: Biomechanics
Forces
____________a push or pull between two objects or bodies. It may involve contact (such
as friction) or it may act at a distance (such as gravity). A force changes or tries to change
the motion of an object or body. e.g. you can push on a door with force. (vector quantity)
Forces are an integral aspect of any study of biomechanics. You can not actually see a force
but you can see and experience its effects (Carr 2004). A force can be described as a push
or a pull that changes or tends to change the shape or state of motion of an athlete or an
object.
Think through an example where a force being applied may not change anything about an
object or its motion:
Answer:
Draw a pin-man drawing of a sportsperson standing still, showing (with arrows) all the
forces acting on him/her. Sketch a second diagram showing all the forces acting on a
runner accelerating and then later on in a race. First one is done for you!
Figure 1.2 Forces acting on a
runner accelerating
Figure 1.1
Forces acting
on a
sportsperson
standing still.
Figure 1.4 Forces acting on a
high jumper just before takeoff.
Figure 1.3 Forces acting on an
athlete later in a race.
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Topic 4: Biomechanics
How the body applies and absorbs Force


The push or pull which causes motion
Measured in newtons (2nd law of motion)
Biomechanics can be defined as the science that examines internal and external forces
acting on the human body and the effects produced by these forces
Internal Force - produced by muscles
● A sprinter running down the track is generating internal forces in the leg muscles
during each stride.
● The net result of these internal forces is a sequence of pushes against the ground
with the foot
External Force:
● With each push against the track (note that the track or ground is an external force),
the ground pushes back against the athlete and so the athlete moves forward.
● Other external/outside forces also act against the athlete such as gravity (vertical
direction downwards towards the centre of the earth) and air resistance (horizontal
motion)
Force can:
● Cause a body at rest to move
● Cause a moving body to slow down, stop, increase its speed or change its direction
● Causes objects to change shape or move (accelerate), has a direction and is
therefore a vector
Examples
●
●
●
●
●
●
Throwing a ball (move)
Catch a ball (stop an object)
Hitting a shuttle cock (change direction)
Speed up when running (change speed)
Wrestling (balance a force keeping it still)
Dribbling a soccer ball (balance another force to keep object moving)
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Topic 4: Biomechanics
1. Think of the vertical forces acting on a high jumper just before take-off.
2. With your thoughts and your understanding of Newton’s Laws of Motion
(research if you don’t know already) to explain why the high jumper is able
to take off.
Watch this video link to help you
Answer:
Forces have both a magnitude and direction which combine to form a force vector. They are
measured in Newtons (N).
5. If the vertical upward ground reaction force on the jumper is 1400 N, and the weight of
the jumper is 600N, estimate the net upward force acting on him/her.
Answer:
 Net upward force F = 1400 - 600 = _______________
Some different types of force in our world are _________force, impulse force, gravitational
force and __________ force. Forces can cause different types of motion (movement) in an
object: (please describe and give examples other than the Tennis Investigation you have
completed).

Linear -

Curvilinear -

Angular (Rotation)-

General-
Remember that gravity acts downwards (towards the centre of the Earth) on all objects on
the surface of the Earth, and the force due to gravity is called the _____________
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4.3.2
Topic 4: Biomechanics
Analyze velocity-time, distance-time graphs of sporting activities.
Motion Graphs
Answer the following questions individually
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Topic 4: Biomechanics
4.3.1 Define the terms displacement, velocity, acceleration, speed, force.
Scalars and Vectors
A scalar quantity is ________________________________
A vector quantity is _______________________________
Define the terms force, speed, velocity, displacement, acceleration, momentum and impulse
as ‘Scalar’ or ‘Vector’ in the table below.
(Go to See http://www.physicsclassroom.com/class/1dkin/u1l1b.cfm)
Scalar
Vector Quantities
Distance and Displacement
Define:
Distance: ______________________________
Displacement: _______________________________
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Topic 4: Biomechanics
Speed and Velocity
Define:
Speed: __________________________________
Velocity: __________________________________
Momentum: _______________________________________
Calculate the following: (show all working)
1. Lionel Messi kicks a ball 6.5 meters. How much time is needed
for the ball to travel this distance if its velocity is 22 meters per
second, south?
2. Andy Murray serves a tennis ball to Rafael Nadal. It travels 9.5
meters south in 2.1 seconds. a. What is the velocity of the tennis
ball?
(b) If the tennis ball travels at constant speed, what is its velocity when Nadal
returns Murray’s serve?
ACCELERATION
Define acceleration: _______________________________________
Calculate the following: (show all working)
1. Michelle Kwan prepares for a jump by increasing her velocity from 2.0
m/s to 10.0 m/s in 3.0 seconds. What is her acceleration?
2. As he climbs a hill, cyclist Bradley Wiggins slows down from 25 km/hr to
6 km/hr in 10 seconds. What is his deceleration?
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Topic 4: Biomechanics
CASE STUDY: Hero or villain? Ben Johnson and the dirtiest race in History
(James Montague, Mon July 23, 2012)
http://www.cnn.com/2012/07/23/sport/olympics-2012-ben-johnson-seoul-1988-dirtiestrace/index.html
Ben Johnson was the last man to settle into his blocks at the Seoul Olympic Stadium. It
was September 24, 1988, a heartbeat before the start of the 100 meters final and what
was to become the most infamous sporting moment in Olympic history. Johnson, like the
rest of an-all star field that included then Olympic champion and fierce rival Carl Lewis,
former world record holder Calvin Smith and future gold medalist Linford Christie, paced
back and forth like caged panthers seeking the psychological advantage of settling last.
The field stretched, hopped and feinted as they pretended not to look at each
other. Johnson merely stared straight ahead, unblinking. Inevitably it was he who
won the first battle. The gun fired and the Canadian leaped -- literally leaped -- from
his starting position into a lead he would never lose.
Just 9.79 seconds later he had smashed the world record in a display of power and awe
never before seen in track and field, against the greatest field of sprinters ever collected.
"Nobody," Johnson recalls in an interview with CNN, laughing in deep, long chugs,
"nobody could touch my start."
What happened next has been seared into the collective memory of the Olympics ever
since. The image of a medal ceremony, more than 24 hours later where Carl Lewis still
can't come to terms with where Johnson had found his extra power; the incredulity on
the faces of the journalists present; the press conference afterward where a triumphant
Johnson eulogized.
"I'd like to say my name is Benjamin Sinclair Johnson Jr, and this world record will last 50
years, maybe 100," he had told the room. Later he said: "A gold medal -- that's something
no one can take away from you."
But they could take it away from him. And they did. Just 24 hours later Johnson had
failed a drugs test when traces of the banned steroid stanozolol were found in his urine.
And after the IOC delegation arrived at his room. Johnson handed the medal back to
the IOC, much to the consternation of his mother. […]
The dirtiest race in history
The scene was set for the greatest 100m final of all time at Seoul. In many respects it
still is, despite the taint of drugs. Only two of the eight runners remained clean
throughout their careers: American sprinter Calvin Smith and the Brazilian Robson da
Silva. But the race, even today, has an explosive power that makes it impossible to
ignore, with four of the field breaking the 10 second barrier. Johnson, perhaps
unsurprisingly, believes it is still the greatest race of all time.
"Regardless what the IOC think, it's definitely the best race ever run even though I
hadn't run my best race yet and you can tell that I have more fuel left in the tank," he
explains before claiming that drugs don't actually make you run faster.
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"You only cheat if no one else was not doing it. I was aware of what other people were
doing in the field. I just did it better than anyone else. It doesn't make you a fast runner
... It was my training regime that was better than the rest of the world. My training
was tailored for Ben Johnson and my coach was a genius. Now the whole world is using
my program."
Johnson will always be a pariah, synonymous with those blistering few seconds when he
flew too close to the sun before crashing back to earth. Yet the experience hasn't
diminished his belief that he still deserves a place among the pantheon of greats.
"The runners today can't compare to what I was running 25 years ago," he claims,
citing better, harder tracks more suited to the modern generation of sprinters. He
believes he would break the 9.5 second barrier if running today.
"No sprinter today could bench-press 395 pounds. In 1987 to '88, I won 25 finals against
the best sprinters and that never happened today. Unbeatable."
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4.3.11
Topic 4: Biomechanics
Explain the factors that affect projectile motion at take-off
or release.
Projectile Motion: Use the vocabulary below to fill in the blanks throughout this
exercise. You may use each of the words or phrases as many or as few times as you need.
Horizontal
Height
Parabolic
Less
Length
Decreases
air pressure
Higher
Length
Projectile
Distance
Air resistance
topspin
poorer
initial vertical velocity
speed of release
height of release
initial horizontal velocity
angle of release
surface to volume ratio
rough
gravity
trajectory
vertical
increases
backspin
1. A ______________ is considered to be any object or body released into the air.
2. All projectiles have a _____________ flight path. The flight path of a projectile is known
as the _____________
3. The ________________ of a projectile consists of a _______________and
_________________ component.
4. The _________________ component gives the projectile _________________ .
5. The _________________ component gives the projectile __________________
For example, if you throw a ball straight up into the air the trajectory has only a
___________ component.
6. When you throw a ball to a friend that is standing 20 metres away from you the
trajectory has a ____________________component as well.
(Label the diagram below).
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Gravity
7. ______________ will affect a projectile as it will decrease the height the projectile can
obtain.
8. The force of ______________ acts on the object to pull it back to earth, limiting the
_______________ component of the projectile.
Air Resistance
1. As a projectile moves through the air it is slowed down by __________________
2. ___________________ will decrease the __________________ component of the
trajectory.
3. The effect of __________________ is relatively small but needs to be considered.
4. A badminton shuttle has greater ___________ than a golf ball as the holes in it
gives it a _________________________
5. Objects with a ______________ surface will also have increased
___________________.
6. _________________: The speed of a projectile also affects _________________ as
friction increases with velocity.
7. The smaller the __________________ of an object, the more air resistance will affect it.
8. This is evident when considering the difference between throwing a feather and a stone.
Extension: Because air resistance affects the horizontal component of a projectiles
trajectory, the effect of it can be minimized by lowering the _______________________
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Speed of Release

Speed or velocity is directly related to distance.

The greater the _________________ the greater the distance covered in flight.
It is divided into two components:
a)
b)
________________________
________________________

Having a higher ___________________ will increase the
_____________________ of the trajectory, resulting in a longer flight path.

This would be an advantage in sports which require good height, such as tumbles
in gymnastics, high jump and ski jumping (tricks).
Extension: give another example here ______________________

Having a higher _____________________ will increase the
_____________________ of the flight time and therefore the distance covered.

This would be an advantage in sports, which primarily require good distance,
such as long jump, ski jumping (distance), and vaults in gymnastics.
Extension: give another example here: ____________________
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Angle of Release

The ______________changes the relationship between the horizontal and vertical
components of a projectile. The ideal ____________is 45 degrees, assuming there
is no ______________and the take off and landing points are the same height.

If the ____________is greater or less than 45 degrees, the distance covered in flight
will be ____________
Extension: In sporting situations the angle of release is often lower, around 35 degrees to
45 degrees. This is because the __________________of the body and because the takeoff
point is usually higher than the landing point, e.g., long jump.
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Height of Release
1. The higher the _____________the greater the _______________covered in
flight. This is because the higher the projectile is released; the longer it will be in
the air.
2. The _______________of the trajectory will be acting on the projectile for longer.
3. An example of this is throwing a javelin. In javelin, to gain more
____________athletes will hold the javelin up ____________ to create a greater
________________.
There is a relationship between height of release and angle of release.
As the height of release ______________ the angle of release _______________
As the height of release_________________, the angle of release ________________
For example, when shooting, basketball players will have a lot lower angle of release than
shorter basketball players to shoot the ball at the same hoop height.
Spin

The amount and direction of _________________acting on a projectile will directly
affect the _____________a projectile will travel.

The reason for this is the _____________acting on the ball.
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Extension example:
1. In a tennis shot, ____________gives poorer distance compared
to___________.
2. A topsin shot creates a region of high pressure on top of the ball and a
region of low pressure below.
3. Air moves from a region of __________ to ____________pressure and as
a consequence the ball will dip suddenly, decreasing the vertical
component of the trajectory. The opposite is true for a backspin.
PROJECTILE MOTION PAST PAPER QUESTION
1.Discuss how the factors that affect projectile motion can influence shot put
technique. (6)
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4.3.7
Topic 4: Biomechanics
Define Newton’s three laws of motion
Newton’s First Law
“An object will remain at rest or continue with constant velocity unless acted on by an
unbalanced force”. This means that bodies or objects stay where they are or keep moving
unless acted on by an unbalanced force. This is sometimes known as the law of inertia.
Outline the forces involved when objects that are thrown or hit on earth and why they do
not continue in their state of motion. Is there an environment where this state of motion
can be maintained forever?
Forces acting on thrown objects
Answer:
The effects that a force has on an object is affected by the mass of the object. If it is a light
object it will be more easily affected as compared to a heavier object. This relates to an
objects resistance to motion. Otherwise known as ______________
E.g. which person has the most inertia or resistance to moving and state why you have
chosen that person?
a. David Beckham – Football player(78kg)
b. Richie McCaw – Rugby player(106kg)
Answer:
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Having a lot of inertia or mass can be an advantage in sport but it can also be a
disadvantage. Think through an advantages and disadvantages of a small or large inertia
and discuss below:
Small Inertia
Advantage
Disadvantage
Rugby
player
Climber
A golf club
Large Inertia
Advantage
Disadvantage
Rugby
player
Climber
A golf club
A common misconception about rock climbing is that it’s all about strength. What is more
important is proper technique, which requires excellent balance and flexibility.
Also, the secret behind rock climbing strength is not absolute power, but power relative to
your own body weight. Rock climbing is one area where size doesn’t matter. What matters
is your ability to pull your own weight.
One consequence of the requirements of rock climbing is that women are often more likely
to have what it takes than men, particularly when it comes to balance and flexibility.
Newton’s Second Law
What is Newton’s 2nd Law
Answer:
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INDIVIDUAL ACTIVITY
Complete the sentences uses the terms ‘faster’ and ‘ slower’ .
1. The greater the force that is applied, the
acceleration.
the
2. The lesser the force that is applied, the
acceleration.
the
3. If the same force is applied to an object with a large mass, it will have a
acceleration.
4. If the same force is applied to an object with a small mass, it will have a
acceleration.
Complete the following calculations
Bradley Wiggin’s bicycle has a mass of 9.1 kilograms. He accelerates at a rate of 1.79
m/s2. Calculate the net force that is accelerating the bicycle.
F = MA
Mo Farah has a mass of 65 kilograms. He produces a force of 84 Newtons between
the ground and his running shoes. How fast does he accelerate?
F = MA
A = F/M
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4.3.2
Topic 4: Biomechanics
Analyze force-time graphs of sporting activities.
Part A: Momentum
Define Momentum:
Answer:
Individual Activity
Calculate momentum for the following problems
Scott Macartney, a US Olympic Ski Team member was going 39 m/s in the downhill ski
race when lost his balance and fell. He has a mass of 65Kg. What was his momentum?
If you can run 6.7 m/s while holding a 3.5 Kg shot put, how much momentum does the
shot put have?
IMPULSE
• Answer the following questions as you watch the video
(http://www.youtube.com/watch?v=qOkvOnLgwrY)
How can you change an object’s momentum?
1. Define impulse
2. Which factor transforms a force into an impulse?
3. What is the relationship between impulse and change in momentum?
4. Why should you follow through when hitting a ball?
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Describe the relationship between linear momentum and linear impulse in the
context of Newton’s Second Law
Calculate impulse for the following problems
1. A football player kicks a ball with a force of 50N. Find the impulse
on the ball if his foot stays in contact with the football for 0.01s.
2. A hockey player applies an average force of 80N to a 0.25kg
hockey puck for a time of 0.2s. Determine the impulse
experienced by the hockey puck.
INDIVIDUAL ACTIVITY
We have seen above that muscular forces can have many effects on objects. Whenever
a force is being applied it always takes time. When a person applies a force over a
certain time then we can say that they have applied an impulse.
How force and time are combined depends on:


the physical capabilities of the person applying the force eg. compare elite
athletes to beginners in a task
the requirements of the task: compare sprinting verses rowing, speeding
something up verses slowing something down ...
Why are the following variables important in maximising impulse?
1.Muscular strength and speed (power):
Answer:
2.Flexibility:
Answer:
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Knowing that the area under the curve equals the impulse that a person has applied look at
the graphs illustrated below and then explain why following through with a bat swing
increases the velocity and potential distance that a ball will travel.
Question
Explain why ‘follow through’ with a bat swing increases the velocity and
potential distance that a ball will travel.
Answer:
In the picture below on the left the ‘goalkeeper’ has kicked the ball with less follow through
(punt). Where as American football player has followed through with their hit.
Answer:
Question
How can spreading a particular force over a greater amount of time be beneficial
to a person/ athlete? Discuss this with specific examples:
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IMPULSE PAST PAPER QUESTION
Q1
Q1a
Q1b
A study was undertaken of Asafa Powell during his 100m sprint for a world
record of 9.74s in Italy in 2007. The graphs below represent the impulse
recorded from a single footfall (from first contact to the foot leaving the
ground). Each graph represents a different stage of the sprint.
Define the term impulse. (1)
Net impulses are a combination of positive and negative impulses. Describe
the net impulse during the 100m sprint for each of the following stages: (1)
i. Early Stage (1)
ii. Middle Stage (1)
iii. Final Stage (1)
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Q1c
Compare the acceleration of Asafa Powell in the early stage to the final
stage of the 100m sprint. (2)
Q1d
Usain Bolt, the winner of the 100m sprint at the 2008 Olympics, reaches
his peak velocity later in the sprint than Asafa Powell.
Using the information above, predict how Usain Bolt’s middle stage force-time
graph would
be different from Asafa Powell’s for the 100m sprint. (2)
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Part B: Velocity: Force-Time graph for a Vertical Jump
Define Impulse: _____________________
The diagrams below show the vertical ground reaction force during the take-off phase of a
vertical jump. Examine the curve and explain what is happening to the jumper at
points A, B, C, D, E and F. (8 marks)
Answer:
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Investigation: Impulse and Impacts
Look at the two graphs in figure 1.1 of Force of impact against time for a baseball bat
striking a ball.
1.1 Force of impact against time for a baseball bat striking a ball.
A Force acting on the ball without follow through.
ball with follow through.
B Force acting on the
1. Explain why follow-through increases the outgoing velocity of the ball.
Answer:
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Topic 4: Biomechanics
Impulse and Impacts: A worked Example
THE FORCE EXERTED DURING A FOOT STRIKE DURING A SPRINT RACE
This example looks at the vertical force exerted on average by a sprinter’s foot on the track
during a 100m sprint. The aim of the calculation will be to estimate the reaction force
produced by a foot contact - which would be the actual force produced by the runner on the
ground.
Consider Figure 1.2 as graphs of force against time for reaction force only (A), and net force
(B).
Figure 1.2 Vertical forces acting on a runner’s foot.
A. Force-time graph for a single foot contact.
B. Force-time graph of net force.

For a male world class 100m sprinter whose time is 10.00s, and whose average
stride length is 2.6m, there are 38.5 strides during the race, and the average time
between foot contacts would be 10.00 = 0.26s.
38.5

The graph shown in figure 1.3 (next page) shows the path of the runner’s centre of
mass against time for two complete strides.

It is estimated that between one fifth and on quarter of the time between complete
strides (0.06s) is that during which a foot is in contact with the ground.

Note that in figure 1.2 above - this corresponds with the time for which force is
applied by a foot on the ground.

In between foot contacts during the unsupported part of the stride, the athlete will fall
towards the ground.
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Figure 1.3 Path of a sprinter’s centre of mass
during two complete strides.

Immediately after a foot
leaves contact, the
athletes centre of mass
will be moving upwards,
then rising towards a
maximum height at half
stride, and falling towards
the next foot contact at an
acceleration produced by
gravity (of g = 10 ms-2).

Therefore during 0.26 0.06 = 0.20 seconds, the
athlete’s centre of mass
will rise towards its peak, then fall again towards the ground (ready for the next foot
contact).
Graphs X,Y and Z (Figure 1.4) show the horizontal ground reaction force versus time traces
for three situations during a 100 metre sprint race.
Figure 1.4 Horizontal ground reaction force versus time in a 100 m sprint.
Note: Positive forces act on the runner in the direction on the run.
Question: Explain how you can tell that graph X represents the horizontal force acting
on the runner during a foot contact just after crossing the finish line. (6 marks)
Answer:
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4.3.8
Topic 4: Biomechanics
Explain how Newton’s three laws of motion apply to sporting
activities.
Define Newton’s Third Law of Motion:
Answer:
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LAW OF CONSERVATION OF MOMENTUM
Define Newton’s Law of Conservation of Linear Momentum:
Answer:
Individual Activity: Conservation of Momentum in American Football
Answer the following questions from the video
http://www.nsf.gov/news/special_reports/football/newtonthirdlaw.jsp
1.Write the formula for the Conservation of Linear Momentum:
2. What is the difference between an elastic and inelastic collision
3. Which type of collision is more common in sport?
4. What are they effects of inelastic collision on an American football player?
Calculating linear momentum
A golfer swings a 0.35 kg club at 30 m/s to hit a 0.04 kg ball off a tee. After impact, his
club speed drops to 25 m/s.
Before impact
Club momentum + Ball momentum
= Total momentum
After impact
Club momentum + Ball momentum
= Total momentum
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4.3.3
Topic 4: Biomechanics
Define the term centre of mass.
Centre of Mass
1. What effects do changes in body
position have on the location of the
centre of mass?
Position of centre of mass
changes as body position
changes.
Answer:
2. How does the jumper change the
position of his/her centre of mass
relative to the centre of his/her torso
during the jump?
Path of centre of mass in a high
jump.
Answer:
3. What is so important about the centre of
mass being below the bar when the athlete jumps over the bar?
Answer :
4. Explain how the position of the centre of mass can lie outside the mass of a body
and give examples from sport of when this is the case.
Answer :
5. Explain why a handstand is a more demanding balance than a headstand.
Answer:
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4.3.5
Topic 4: Biomechanics
Distinguish between 1st, 2nd and 3rd class levers.
Part A: Levers
A lever is basically a rigid structure, hinged at some part and to which forces are applied at
two othe rpoints.
A lever consists of three parts (as defined above). What are they?
1.
2.
3.
Functions
Levers perform two main fucntions: What are they?
1.
2.
Classes of Lever
There are three types of lever systems. Define these below and provide examples
of them in action:
Class
1st
2nd
3rd
Illustration
Definition
Example
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1. Label all the levers below:
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Part B: Levers in the Human Body
Class
Example in the body
INDIVIDUL ACTIVITY – LEVERS IN SPORT
Identify the effort, fulcrum and load in the examples given below
1. Triceps-elbow joint
1. The action occurring at the triceps/ elbow joint.
Effort (agonist):
Load (resistance):
Fulcrum (axis):
Class of lever:
Bones involved:
Name the antagonist muscle:
Example in sport
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2. Calf-ankle joint
Effort (agonist):
name the antagonist muscle:
Load (resistance):
Fulcrum (axis):
Class of lever:
Bones involved:
A second-class lever is a type of lever in the human body; one example is the Achilles tendon,
pushing or pulling across the heel of the foot. Such connections between joints, called synovial
joints, are fulcrums, the bones they connect are levers, and the muscles attached to them apply
force (or resistance).
The body acts as second-class lever when one engages in a full-body push-up. The foot is the
fulcrum, the body weight is the resistance, and the effort is applied by the hands against the
ground.
3. Biceps-elbow joint
1. The action occurring at the biceps/ elbow joint.
Effort (agonist):
name the antagonist muscle:
Load (resistance):
Fulcrum (axis):
Class of lever:
Bones involved:
IB
Sports, Exercise
and Health
Science
4.3.9
Topic 4: Biomechanics
State the relationship between angular momentum, moment of inertia and
angular velocity
Part A: ANGULAR MOMENTUM
1. Why is angular momentum important in figure skating?
Answer:
2. What is the relationship between angular momentum and angular velocity?
Answer:
3. How can vertical velocity be increased during a take off? Which Laws of Motion does
this refer to?
Answer:
4. What is the relationship between the position of the arms and the rotational
velocity?
Answer:
5. Which Law of Physics does the following principle refer to? (see picture)
Answer:
IB
Sports, Exercise
and Health
Science
Topic 4: Biomechanics
ANGULAR KINETICS
Part B: Angular Momentum Moment of Inertia and Angular Velocity
Because all levers produce rotation around an axis, they also produce torque. Torque is defined as
___________________.
A force that does not pass through the centre of gravity of the body on which it acts or through a
point at which the body is fixed. Such a force produces translation and rotation. Its rotatory effect is
known as torque.
1.How can we apply this to sporting situations when we consider how we cause a ball to spin.
Consider volleyball and how we apply topspin, or backspin.
Where do we hit the ball?
Draw in the force, the COG and resulting rotation from topspin and backspin force on a volleyball.
2. What can we do to make the ball spin faster?
So basically the greater the force applied, the greater the ____________________.
The longer the lever used, the greater the _____________________.
See http://protabletennis.net/content/topspin-and-backspin
IB
Sports, Exercise
and Health
Science
Topic 4: Biomechanics
Linear vs Angular Kinematics: Fill in Angular motion on the comparison table.
Linear Motion
Angular Motion
Acceleration
Angular acceleration
Velocity
Displacement
Momentum
Force
Torque
Inertia
Newton’s second law
Can you rewrite Newton’s 3 Laws to make them applicable to angular motion?
Law
Explanation
IB
Sports, Exercise
and Health
Science
4.3.10
Topic 4: Biomechanics
Explain the concept of angular momentum in relation to sporting activities
Conservation of angular momentum in a pike dive
If a person or object such as a ball is spun they will continue to spin provided that there is no
force(s) acting to stop this.
Frequently forces such as friction act on us and slow the spinning down – however in instances
such as during the rotating/ somersaulting of gymnasts or divers – the air resistance in these
activities is actually quite small that it is nearly negligible.
Also, when a person has jumped into the air they are unable to change their angular momentum
as there is nothing for them to push against. This means that the persons angular momentum is
conserved (stays the same) during the flight involved in their action.
Fill in the blanks using key terms from the word bank:


Moment of _____________________and angular velocity interrelate in _____________
movements because angular momentum is _______________
when
an athlete is off the ground, or near to constant when on a surface with low
_________________ eg ice skating rink).
As angular momentum is constant when airborne, moment of inertia and angular velocity are
_____________ As one ____________________ the other______________________.
.
increases
friction
aerial
proportional
inversely
Inertia
constant
decreases
Delete the incorrect option below:
When the mass is moved closer to the axis of rotation, the moment of inertia
increases/decreases, and the angular velocity increases/decreases. This means that the
object spins faster.
IB
Sports, Exercise
and Health
Science
Topic 4: Biomechanics
When the mass is moved further from the axis of rotation, the moment of inertia
increases/decreases, and the angular velocity increases/decreases. This means that the
object spins slower.
Conservation of angular momentum in a somersault:
In the spaces provided discuss what happens to moment of inertia and angular velocity for each of
the body positions.
Angular momentum
=
Moment of inertia
X
Angular velocity
Conserved throughout the flight
time irrespective of body position.
BODY POSITION
OF ATHLETE
Tucked
Long
????????????
?????????????
????????????
?????????????
The illustration below shows the interrelationship between angular velocity, moment of inertia and
angular momentum.
IB
Sports, Exercise
and Health
Science
Topic 4: Biomechanics
a.
In biomechanical detail, explain the relationship that occurs between moment of inertia
and angular velocity as the diver executes the tucked backward one and a half dive. (6
marks)
Answer:
b.
Explain why angular momentum remains constant throughout the dive? (1 mark)
Answer:
c.
Let us assume that the diver over-rotates in the dive. Explain biomechanical detail what
may have happened in order for this to occur. (2 marks)
Answer:
In biomechanical terms, explain why a gymnast must tuck tightly when performing a triple
somersault.

The tuck reduces the moment of inertia ( and as angular momentum is conserved in airborne
activities ) thereby increasing the angular velocity and allowing the gymnast to spin quickly
and complete the three rotations.
For the landing, why does the gymnast performing a triple somersault straighten the body ?

Straightening the body increases the moment of inertia thereby slowing the speed of rotation
and allowing the gymnast to land without over rotating and falling over.
IB
Sports, Exercise
and Health
Science
Topic 4: Biomechanics
Conservation of momentum Past Paper Questions
1. Why do shot-putters use either the glide or a spin technique prior to the
release of the shot (4 marks)
Answer:
2. Explain how a gymnast can alter the speed of rotation during flight. (7 marks)
Answer:
IB
Sports, Exercise
and Health
Science
4.3.12
Topic 4: Biomechanics
Outline the Bernoulli principle with respect to projectile motion in sporting
activities
FLUID DYNAMICS
Define the following key terms
Key term
Fluid
Drag
Surface drag
Form drag
Wave drag
Boundary layer
Bernoulli’s
principle
Magnus effect
Definition
Example
IB
Sports, Exercise
and Health
Science
Topic 4: Biomechanics
Question: Explain why golf balls have dimples.
Answer:
IB
Sports,
Exercise and
Health Science
Topic 4: Biomechanics
Magnus Effect
Explain Roberto Carlos swerving free kicks with regards to the Magnus Effect.
http://www.real-world-physics-problems.com/physics-of-soccer.html
Answer: