Download MOTION, FORCES, AND SIMPLE MACHINES!

MOTION, FORCES, AND SIMPLE
MACHINES!
Explore Activity

Release the ball from a point near the bottom of the
curve.
Describe the motion.
How high does it go?
When is its speed the greatest?

Release the ball from a point near the top of the curve.
Describe the motion.
How high does it go?
When is its speed the greatest?

Compare your results.
I. Motion
 To describe how fast a
bike is traveling, you
must know two things
about its motion:
1. The distance it has
traveled
2. How much time it
took to travel that
distance.
A. Average Speed
 Average speed = Total distance traveled
travel time
s = speed, d = distance, and t = time
s = d_
t
Speed cont.
 Because average speed is always calculated by
dividing distance by time, its units will always be
a distance unit divided by a time unit.
 EX:
Speed of a car? Miles / hour
Calculating Average Speed
 Riding your bike, it takes you 30 minutes to get
to your friend’s house, which is 9 km away.
What is your average speed?
 SOLUTION:
 What you know:
d = 9 km
t = 30 min = 0.5 h
 What you NEED to know: s
 Equation you will use:
s = d/t
 Substitute in values:
s = 9 km / 0.5 h
ANSWER
s = 18 km / h
Calculating Average Speed PRACTICE
 If an airplane travels 1,350 km in 3 h, what is its
average speed?
 SOLUTION:
 What you know:
 What you NEED to know:
 Equation you will use:
 Substitute in values:
 ANSWER
d = 1,350 km
t=3h
s
s = d/t
s = 1,350 km / 3h
s = 450 km / h
B. Instantaneous Speed
 Average speed is useful when you don’t need to
know details of the motion.
 EX: a car trip…..traffic lights, traffic jam, high
speed highway….
 What if you want to know your speed at a certain
time?
 Instantaneous speed: the speed of an object at
any instant of time.
(in a car, how is your instantaneous speed given?)
B. Instantaneous Speed cont.
 How is instantaneous speed different from
average speed?
C. Constant Speed
 Constant Speed is when an object’s
instantaneous speed does not change.
 At a constant speed, average speed and
instantaneous speed are the same!
D. Distance
 If an object is moving with constant speed, you
can use the equation you used for speed to
calculate distance!
s = d
speed = distance / time
t
d = s x t
distance = speed x time
Calculating Distance
A marathon runner can maintain a constant speed of 16
km/h, how far can she run in 24 min (0.4 h)?
 SOLUTION:
 What you know:
s = 16 km/h
t = 0.4 h
 What you NEED to know:d
 Equation:
d=sxt
 Substitute values
d = 16 km/h x 0.4 h
 SOLUTION
d = 6.4 km
NOTICE: units of time in the speed MUST be the same as
the time or they won’t cancel! If they aren’t the same in
your problem, you must convert!

Calculating Distance
It takes your family 2 h to drive to Idlewild Park at an
average speed of 73 km/h. How far away is the park?
 SOLUTION:
 What you know:
s = 73 km / h
t=2h
 What you NEED to know:d
 Equation:
d=sxt
 Substitute values
d = 73 km/h x 2 h
 SOLUTION
d = 146 km

E. Velocity
You are walking down the street at a constant
speed heading north. You turn when you reach an
intersection and start walking with the same speed,
but you are now heading east.
 You motion has CHANGED even though your
speed is the same.
 To describe your motion,
you need to tell not only how
fast you were going but in
what direction.

E. Velocity
 Velocity:
the speed of an object and its direction
of motion.
 Velocity changes when speed changes, the
direction of motion changes or both change!
 When you turned the corner, even though your
speed didn’t change, your direction did, SO your
velocity changed.
F. Acceleration
 You’re skateboarding the half-pipe.
 At the top, you are at rest, your speed is zero.
 When you start down, you smoothly speed up,
going faster and faster.
 If the angle of the half-pipe were steeper, you
would speed up at an even greater rate.
F. Acceleration
 Speed describes how distance traveled changes
with time.
 Acceleration describes how velocity changes
with time.
 Acceleration is the change in velocity divided by
the time needed for the change to occur.
F. Acceleration
Marble
Acceleration
Acceleration
Marble
Marble
Ramp
Ramp
A marble rolling down a
hill speeds up. Its motion
and acceleration are in the
same direction.
Ramp
This marble is rolling on a level
surface with constant velocity.
Its acceleration is zero
A marble rolling up a hill
slows down. Its motion
and acceleration are in
opposite directions.
Calculating Acceleration
 If the direction of motion is not changing, motion
is in a straight line and you can use this formula
to calculate acceleration:
 Acceleration = change in speed / time
a = acceleration, t = time
si = initial speed, sf = final speed
a = (sf – si)
t
Calculating Acceleration
If an object at rest accelerates to a final speed of 10 m/s
in 2s, what is the acceleration?
 What you know:
si (initial speed) = 0 m/s
sf (final speed) = 10 m/s
t=2s
 What you want to know: a = ?
 FORMULA:
a = (sf – si)
t
Substitute in Values:
a = (10m/s – 0m/s)
2s
SOLVE:
a = 5m/s2

Calculating Acceleration
You are sliding on a snow covered hill at a speed of
8m/s. There is a drop that increases your speed to 18
m/s in 5s. Find your acceleration.
 What you know:
si (initial speed) = 8 m/s
sf (final speed) = 18 m/s
t=5s
 What you want to know: a = ?
 FORMULA:
a = (sf – si)
t
Substitute in Values:
a = (18m/s – 8m/s)
5s
SOLVE:
a = 2 m/s2

Calculating Acceleration
 Practice Problem:
 The roller coaster you are on is moving at 10 m/s.
5 s later, it toes a loop-the-loop and is now
moving at 25 m/s. What is the roller coaster’s
acceleration over this time?
Calculating Acceleration
 What you know:
si (initial speed) = 10 m/s
sf (final speed) = 25 m/s
t=5s
 What you want to know:
a=?
 FORMULA:
a = (sf – si)
t
Substitute in Values:
a = (25m/s – 10m/s)
5s
SOLVE:
a = 3 m/s2
Graphing Speed
 The acceleration of an object can be shown on a
speed – time graph.
When the acceleration
is zero, the speed
S
p
e
e
d
remains constant.
As you skate down hill, the speed
increases when the acceleration is
in the direction of the motion.
TIME
When the acceleration is
in the opposite direction
as the motion, the speed
decreases.
PRACTICE
1. During rush-hour traffic in a big city, it can take 1.5 h to
travel 45 km. What is the average speed in km / h for
this trip?
2. A car traveling 20 m/s breaks and takes 3 seconds to
stop. What is the acceleration in m/s?
3. A runner accelerates from 0 m/s to 3m / s in 23 s. What
is the accelerations.
4. If an airplane is flying at a constant speed of 500 km /h.
Can it e accelerating? Explain.
5. Describe the motion of a skateboard as it accelerates
down one side of a half-pipe and up the other side. What
would happen if the upside of the up side pipe were not
as steep as the downside?
Section 2
Newton’s Laws of Motion
Objectives:
 Describe how forces affect motion
 Calculate acceleration using Newton’s second
law of motion
 Explain Newton’s third law of motion
Force
 A force is a push or a pull.
 Forces are what cause objects to move.
 Force is measured in newtons (N)
One newton is about the amount of force it would
take to lift a Quarter-Pounder.
Force and Acceleration
 Exerting a force on an object causes its motion
to change.
 THEREFORE: Forces cause objects to
accelerate.
 (an object has acceleration when it’s speed or
direction of motion changes.)
 Anytime a force acts on something, its speed
changes or its direction of motion changes, or
BOTH change.
After a ball is thrown, it follows a curved path toward
the ground. How does this curved path show that the
ball is accelerating?
Balanced and Unbalanced
Forces
 If more than one force is acting on an object and
does not cause the objects motion to change, it
is a balanced force.
Balanced forces cancel each other out.
 If more than one force is acting on an object and
it’s motion DOES change, the forces are
unbalanced.
Unbalanced forces DO NOT cancel each other out.
Example – Balanced Forces
Example – Unbalanced Forces
Combining Forces
 When more than one force acts on an object, the
forces combine
 The combination of all of the forces acting on an
object is called the net force.
Net Forces
 If forces are in the same direction, they add
together to form the net force.
 If forces are in opposite directions, the net force
is the difference between the two forces and is in
the direction of the larger force.
Net Forces
Net Forces Practice
Gravity
 If you hold a basketball shoulder height then let it
go, what force pulls it to the ground?
 Gravity of course!
 Gravity is defined as the pull that all objects
exert on each other.
 When you drop the basketball, the gravitational
force between the ball and Earth, pulled it toward
the Earth.
Gravity
 Objects don’t have to be touching to exert
gravitational force on each other.
 The gravitational force between two objects gets
weaker as the objects get further apart.
 Also, the gravitational force is weaker between
objects of less mass – like you and your desk,
compared to objects of greater mass like you
and the Earth.
Gravity!
Less Gravitational Force between
objects of smaller mass.
More gravitational Force between
an object of small mass and one
of large mass.
More Gravitational Force
between objects that are close
together.
Less Gravitational Force between
objects that are further apart.
Newton’s First Law of Motion
 An object in motion stays in motion and an
object at rest stays at rest until a force acts on it.
 This means, an object’s motion won’t change
unless a force acts on it.
 EX:
Your paper stays on your desk, unless you
pick it up or a breeze blows it.
Newton’s First Law of Motion
 Also, an object in motion continues to stay in a
constant motion, unless a force acts on it.
 WAIT! Say I throw a football….it eventually falls
to the ground…
 But I thought objects in motion stay in motion…
 What force acted on the football?
 GRAVITY!
Friction
WAIT! Newton’s first law says that a moving object
should never slow down or change direction until a
force acts on it.
 BUT if you push a book across the table, it slows down
to a stop! WHY?
 FRICTION! This is the force that acts on it and causes
it to stop.
 Friction is a force that resists motion between two
surfaces that are in contact. It always acts in the
opposite direction to motion.
 To keep an object moving when friction is acting on it,
you have to keep applying force!

Friction cont.
 Friction is caused by the roughness of the
surfaces in contact.
 A rougher surface will cause more friction and a
smoother surface will cause less friction.
 EX: if you push a hockey puck on ice it will
travel further before it stops than if you push it on
carpet.
Inertia and Mass
 How easy would you say it is to move a
refrigerator?
 Pretty difficult huh?
 How about stopping a person on a skateboard
who is much bigger than you are?
 Ouch.
Inertia and Mass
 When moving or stopping a big object, the object
resists a change in motion.
 Inertia, is the tendency of an object to resist
motion – this is another way to state Newton’s
first law of motion. The Law of Inertia
 The more matter an object has the more inertia it
has!
Newton’s Second Law of Motion
 Newton’s first law says that a change in motion
won’t occur unless there is a net force large
enough to move the object or stop an object that
is moving.
 Newton’s SECOND law tells how a net force
acting on an object changes the motion of an
object.
Newton’s Second Law of Motion

Newton’s second law says:
A net force changes the velocity of the object and causes it to
accelerate.

This includes two things:
1.
2.
IF an object is acted on by a net force, the change in velocity
will be in the direction of the net force.
Acceleration can be calculated from the following equation:
F (force)
in Newtons
F=mxa
m (mass)
 in kilograms
a(acceleration)
in meters per
second squared.
Mass and Acceleration
 When a net force acts on an object, it’s
acceleration depends on the mass of the object!
 The more mass an object has, the more force is
necessary to cause it to accelerate!
 EX: it’s much harder to move a refrigerator than
it is to move an empty shopping cart,
BECAUSE – the refrigerator has more mass.
Mass and Acceleration cont.
 With the same force acting on a refrigerator and
an empty shopping cart, the refrigerator will have
LESS acceleration than the empty cart.
 MORE MASS = LESS ACCELERATION with the
same amount of force.
Newton’s Third Law of Motion
 Remember when Ms. Smyder pushed the wall?
 You might be surprised to know….THE WALL
PUSHED BACK!
 Well…the wall isn’t alive, but Netwon’s Third Law
says:
 When one object exerts a force on a second
object, the second object exerts an equal force
in the opposite direction.
Newton’s Third Law of Motion
 EXAMPLE: When you walk, you push down on
the sidewalk and it pushes back up on you with
an equal and opposite force.
 The force exerted by the first object is the action
force, the force exerted by the second object is
the reaction force.
Newton’s Third Law of Motion
ACTION
REACTION
Force Pairs Act on Different
Objects
IF forces always act in equal but opposite pairs, you
might ask – HOW CAN ANYTHING EVER MOVE??
 Won’t forces acting on an object always cancel each
other out?
 REMEMBER, equal and opposite forces act on
DIFFERENT objects.
 When you push on a book, a force is acting on the
book. When it pushes back on you, the force is acting
on you!

Examples of Newton’s Third Law
 Imagine you are jumping off of a small boat.
 You are pushing back on the boat with your feet
and the same force is pushing you forward.
 Since you have more mass than boat, it will
accelerate more and move farther than you do.
Examples of Newton’s Third Law
 This would be the opposite if you jumped off of a
bigger boat.
 Since the boat has so much more mass, the
force that you exert on the boat only gives a tiny
acceleration – in fact, you probably won’t notice
the boat moving at all. BUT the force the boat
exerts on you might easily propel you to the dock
near you.
Section 2 - Practice
1. Make a table listing Newton’s laws of motion. For
each law, include the definition and give at least one
example from your everyday life. Do not use examples
from the notes!!!!
 2. Does a force act on a car if it moves at a constant
speed while turning? Explain.
 3. You throw a ball to your friend. If the ball has a mass
of 0.15 kg and it accelerates at 20 m/s2, what force did
you exert on the ball?
 4. Give at least two examples of using inertia to your
advantage.
 5. Newton’s third law is a good example of cause and
effect. Explain why, using a ball bouncing off of a wall
as an example.

Section 3
Work and Simple Machines
Define Work
Distinguish the different types of
simple machines
Explain how machines make work
easier
Work
 Newton’s Laws explain how forces change the
motion of an object.
 When you apply an upward force on a box, it
moves UP!
 What is work??
Work cont…
 In science, WORK is done when a force causes
an object to move in the same direction that the
force is applied.
Effort doesn’t always Equal Work
Remember when Ms. Smyder pushed the wall?
She tried really hard! But the wall didn’t move.
 In order for WORK to be done, two things MUST
happen:
1. A force must be applied on an object
2. The object must move in the direction of the
force.
If the object doesn’t move, no work was done.
So, did Ms. Smyder do work when she pushed the
wall?
NO!

 Imagine you are lifting a box.
You can feel your arms exerting a force as you lift
upward.
The box moves upward, in the direction of your
force.
YOU HAVE DONE WORK!
 Imagine you carry the box forward.
You can still feel your arms applying an upward
force on the box.
BUT the box is moving forward….not up.
NO WORK IS BEING DONE BY YOUR ARMS!
Because the motion is not in the same direction as
the force.
Calculating Work
 The greater the force applied that makes an
object move, the more work is done.
 Which of these tasks would involve more work?
 Lifting a shoe from the floor to your waist
OR
 Lifting a pile of books the same distance
Calculating Work cont…
 Even though you lifted them the same distance,
more work is done when you lift the books
because it takes more force to lift them!
You can calculate work:
work = force x distance
W = F x
d
Calculating Work cont…
Force is measured in newtons (N)
Distance is measured in meters (m)
Work is measured in joules (J)
Energy is also measured in joules. Named for
James Prescott Joule, a 19th century physicist
who showed that work and energy are related.
Calculate Work
 A weight lifter lifts a 500 N weight a distance of 2 m
from the floor to a position over his head. How
much work does he do?
 Know:
Force = F = 500 N
distance = d = 2 m
 Want to know: work = W
 Equation:
W=Fxd
 Substitute:
W = 500 N x 2 m
 Solve:
W = 1000 J
PRACTICE
 Using a force of 50 N, you push a computer cart
10 m across a classroom floor. How much work
did you do?
Know:
F = 50 N
d = 10 m
Want to Know: W
Equation:
W=Fxd
Substitute:
W = 50 N x 10 m
Solve:
W = 500 J
What is a Machine?
 A machine is a device that you use that makes
work easier.
 A can opener changes a small force applied by
your hand into a larger force and makes it easier
to open the can.
Simple Machines
 A simple machine is a machine that uses only
one movement.
 The following are Simple Machines:
1. Inclined Plane
2. Wedge
3. Screw
4. Lever
5. Wheel and axle
6. Pulley
Simple Machines
 EX:
 A screwdriver is a simple machine, it only
requires one movement – to turn it!
Compound Machines
 A compound machine is a combination of simple
machines.
 A can opener is an example of a compound
machine – it combines several simple machines.
 Machines make work easier in two ways:
1. They can change the size of a force applied
2. They can also change the direction of the
force.
Mechanical Advantage
 The number of times the applied force is
increased by a machine is called the mechanical
advantage.
 When you push on the handles of the can
opener, the force that you apply is called the
input force (Fi).
 The can opener changes your input force to the
force that is exerted by the metal cutting blade
on the can. The force exerted by a machine is
called the output force (Fo).
Mechanical Advantage
 Mechanical advantage is the ratio of the output
force to the input force:
Mechanical advantage = Output force
input force.
MA = Fo / Fi
Work in and Work out
 In a simple machine, the input and the output
force do work:
You push on the handles of a can opener and the
handles move – work is done (input)
The blade of the can opener moves down and
punctures the can – work is done (output)
 In an ideal machine, there is no friction.
Increasing Force
A simple machine can make a small input force into a
larger output force.
W=Fxd
 SO if work in is equal to work out, a smaller input force
must be applied over a larger distance than the larger
output force.
 Think about that can opener, it increases the force that
you apply to the handle SO the distance you move the
handle is large compared to the distance the blade of
the can opener moves as it pierces the can.
 In all real machines, friction always occurs as one part
moves past another.

The Pulley
The Lever
The Wheel and Axle
The Inclined Plane
The Wedge
The Screw
Practice!
1.
2.
3.
4.
5.
How much work would it take to lift a 1,000 kg
limestone block 146 m to the top of the Great
Pyramid?
Explain how you can tell if work is being done on an
object.
Using a pulley system with a mechanical advantage
of 10, how large an input force would be needed to
lift a stone slab weighing 2,500 N?
Compare a wheel and axle to a lever.
Identify two levers in your body. What class of lever
is each?