Download CHAPTER 4 – LEVERS

SECTION A –
CHAPTER 4
ANSWERS TO QUESTIONS
CHAPTER 4 – LEVERS
Text between pages 69 and 71, answers to questions on page 71 of the text book.
1) Sketch the lever system which would represent the action of the biceps muscle in flexing the arm. Show on your diagram
the resistance arm of the lever. 3 marks
figure 4.11 – the elbow and
Answer
forearm lever
• See figure 4.11.
•
•
•
•
E is the effort force in the biceps muscle.
L is the load force applied at the hand.
The triangle is the pivot or fulcrum of the lever.
The resistance arm is the structure (forearm) between hand (load) and elbow
(fulcrum).
figure 4.7 – long jumper taking off
2) In figure 4.7 of a jumper taking off,
name, sketch and label the lever
system operating at knee B during
this action.
3 marks
Answer
• See figures 4.12 and 4.13.
• This is a class 3 lever (effort between
pivot and load).
• Note that the effort (figure 4.12)
is transmitted to the tibia via the
patella tendon, which passes over
the knee and inserts below the joint
(figure 4.13).
B
E = effort
B
L = load
fulcrum (pivot)
figure 4.13 – jumper’s knee 2
figure 4.12 – jumper’s knee 1
effort force
in quadriceps
muscle
fulcrum (pivot)
at knee joint
load force
on foot
fulcrum (pivot)
at knee joint
load force
on foot
effort force in
quadriceps muscle
via patella tendon
figure 4.8 – softball bat
3) In softball, what order (class) of lever is shown in the hitting action in figure
4.8?
State one disadvantage and one advantage of reducing the bat length for a
beginner.3 marks
Answer
• This is a class 1 lever.
Advantage of shortening bat length is:
• Learning the skill involved may be easier - since the strike point is nearer the
hand.
Disadvantage of shortening the bat would be:
• Less force can be applied as a load for a given effort, hence the strike on the ball
would impart less speed to the ball.
22
bat
fulcrum
(pivot)
weight
effort
APPLIED EXERCISE PHYSIOLOGY
4) Name, sketch and label the lever system which is operating at the ankle of leg C when doing the sprint set action illustrated
in figure 4.9.
3 marks
figure 4.9 – a sprint start
C
C
figure 4.14 – ankle foot lever
effort force in
calf muscles
Answer
• See figure 4.14.
• This is a class 2 lever.
• Note that the load force is a combination of the weight of the athlete acting downwards
through the tibia and fibula on the ankle joint, and the reaction to the accelerating force
driving the sprinter forwards.
figure 4.10 – a press-up
A
load force
on foot
fulcrum (pivot)
under ball of foot
5) a)
Figure 4.10 shows an elbow joint A of a person performing an exercise.
Draw a simplified sketch to Show the lever system, indicating the various forces operating.
4 marks
A
Answer
• Figure 4.15 – this is a class 2 lever.
• Normally the triceps elbow system is a class 1 lever, but here, the pivot is at the
hand as shown, which forces the system into class 2 lever shape.
figure 4.15 – elbow triceps lever
effort force in
triceps muscle
effort arm
b) On your diagram draw and label the effort and resistance arm. 3 marks
Answer
• Resistance arm lies between pivot and weight force (the lever arm is at right angles
to the force).
• Effort arm lies between point of elbow and pivot.
resistance arm
fulcrum (pivot)
under heel of hand
load force
(weight of athlete
acting downwards
via humerus
on elbow)
6) During physical activity the performer uses a combination of levers to produce movement. Explain why the length of the
lever will affect performance. 3 marks
Answer
• The longer the lever (usually length of limb - the resistance arm) the greater the speed at the load (end of limb).
• The longer the lever the less effort required.
• Shorter levers generate more force (compare compact small gymnasts or weight lifters with taller performers).
• Class 1 levers are used to generate speed.
• Class 2 levers are more efficient because the effort is further away from the pivot (example - the ankle joint with calf muscles).
Chapter 4 - levers 23