This ppt was created by Dr Beka a lecture from Ekwendeni College of Health Sciences (ECoHS) Ekwendeni Mzimba Malawi. It is understandable and easy to read for students who are studying clinical medicine

1. Force and Motion Standards
• S8P3 Students will investigate the
relationship between force, mass, and the
motion of objects.
• a. Determine the relationship between
velocity and acceleration.
• b. Demonstrate the effect of balanced and
unbalanced forces on an object in terms of
gravity, inertia, and friction.

2. What do we need to know and
be able to do?
I CAN explain how the quantity and direction
of velocity and acceleration related,
I CAN identify all forces acting on objects in
motion or at rest.
I CAN explain the advantages of using each
of the six simple machines to do work.
I CAN predict changes in gravitational force
as a result of changes in mass and/or
distance.

3. • What is the relationship between
velocity and acceleration?
Supporting Questions:
• How can motion of an object be
determined by a graph?
Essential Question:

4. Speed, Velocity, and Acceleration

5. Goals:
• To investigate what is needed to describe
motion completely.
• To compare and contrast speed and
velocity.
• To learn about acceleration.

6. To describe motion accurately and completely, a frame of reference is needed.

7. An object is in motion if it changes
position relative to a reference point.
• Objects that we call stationary—such as a
tree, a sign, or a building—make good
reference points.
The passenger can use a tree as a reference point to decide if the
train is moving. A tree makes a good reference point because it is
stationary from the passenger’s point of view.

8. Describing Motion
Whether or not
an object is in
motion depends
on the reference
point you choose.

9. Distance
When an object moves, it goes from point
A to point B – that is the DISTANCE it
traveled. (SI unit is the meter)
Distance is how much ground an object has
covered during its motion.
A
B

10. Displacement
Knowing how far something moves is not sufficient. You
must also know in what direction the object moved.
Displacement is how
far our of place the
object is; it is the
object’s overall
change in position.

11. • It is a rate!
• What does that
mean?
• A change over time.
What is the change?
• Change in position, in
other words, distance.
• Standard unit: meters
per second (m/s)

12. • Average speed – rate
for the duration of an
entire trip
• This can be
calculated…ready for
the equation?
• v = d/t
• v – velocity
• d – distance
• t – time
• What units do we
use?
• Try the practice
problems.

13. Speed
Calculating Speed: If you know the distance an
object travels in a certain amount of time, you
can calculate the speed of the object.
Speed = Distance/time Average speed = Total distance/Total time
What is
instantaneous
speed?
Instantaneous
speed is the
velocity of an
object at a
certain time.

15. Because velocity depends on direction as well
as speed, the velocity of an object can change
even if the speed of the object remains
constant.
Velocity
2.1
Describing Motion
The speed of this car
might be constant,
but its velocity is not
constant because the
direction of motion
is always changing.

16. Velocity
Velocity is a description of an object’s
speed and direction.
As the sailboat’s direction
changes, its velocity also
changes, even if its speed stays
the same. If the sailboat slows
down at the same time that it
changes direction, how will its
velocity be changed?

17. Speed v. Velocity
1. How are speed and velocity similar?
They both measure how fast something is moving
2. How are speed and velocity different?
Velocity includes the direction of motion and
speed does not (the car is moving 5mph East)
3. Is velocity more like distance or
displacement? Why?
Displacement, because it includes direction.

18. Graphing Speed
D
I
S
T
A
N
C
E
T I M E
Speed
increasing
Object is
stopped
Object begins moving at
a different speed

19. The steepness of a line on a graph is called
slope.
• The steeper the slope is, the greater the
speed.
• A constant slope represents motion at
constant speed.
Using the points shown, the rise is
400 meters and the run is 2 minutes.
To find the slope, you divide
400 meters by 2 minutes. The slope is
200 meters per minute.

20. Formula for Calculating Speed
Speed = Distance time

21. Problem Solving: Calculating
Speed
What is the speed of a sailboat that is traveling 120 meters in 60 seconds?
Step 1: Decide what the problem is asking? A boat traveled 120 meters in 60
seconds. What was the speed of the boat?
Step 2: What is the formula to calculate speed? Speed = Distance/Time
Step 3: Solve the problem using the formula:
Speed = 120 meters 60 seconds = 2 m/s
So, the boat was traveling at 2 m/s
Now you try:
What is the speed of a car that is traveling 150
miles in 3 hours?

22. Answer:
Step 1: What are the facts in the problem?
A car is traveling 150 miles in 3 hours.
Step 2: What is the formula to solve the
problem? Speed = Distance/Time
Step 3: Solve the problem.
Speed = 150 miles 3 hours
Speed = 50 miles/hr.
So, the car is traveling 50 miles/hr.

23. Acceleration
Acceleration is the rate at which velocity
changes.
Acceleration can result from a change in
speed (increase or decrease), a change
in direction (back, forth, up, down left,
right), or changes in both.

28. • The pitcher throws. The ball speeds toward the
batter. Off the bat it goes. It’s going, going, gone! A
home run!
• Before landing, the ball went through several changes
in motion. It sped up in the pitcher’s hand, and lost
speed as it traveled toward the batter. The ball
stopped when it hit the bat, changed direction, sped
up again, and eventually slowed down. Most examples
of motion involve similar changes. In fact, rarely does
any object’s motion stay the same for very long.

29. 1. As the ball falls from the girl’s hand, how does its
speed change?
Understanding Acceleration
2. What happens to the speed of
the ball as it rises from the ground
back to her hand?
3. At what point does the ball
have zero velocity? When it
stops and has no direction.
4. How does the velocity
of the ball change when
it bounces on the floor?

30. You can feel acceleration!
If you’re moving at 500mph
east without turbulence,
there is no acceleration.
But if the plane hits an air pocket and drops 500 feet in
2 seconds, there is a large change in acceleration and
you will feel that!
It does not matter whether you speed up or
slow down; it is still considered a change in
acceleration.

31. In science, acceleration refers to increasing speed,
decreasing speed, or changing direction.
• A car that begins to move from a stopped position or speeds
up to pass another car is accelerating.
• A car decelerates when it stops at a red light. A water skier
decelerates when the boat stops pulling.
• A softball accelerates when it changes direction as it is hit.

32. Calculating Acceleration
Acceleration = Change in velocity
Total time
So…Acceleration = (Final speed – Initial speed)
Time

33. As a roller-coaster car starts down a slope, its
speed is 4 m/s. But 3 seconds later, at the
bottom, its speed is 22 m/s. What is its
average acceleration?
Calculating Acceleration
What information have you
been given?
Initial speed = 4 m/s
Final Speed = 22 m/s
Time = 3 s

34. What quantity are you trying to calculate?
The average acceleration of the roller-coaster car.
What formula contains the given quantities and the
unknown quantity?
Acceleration = (Final speed – Initial speed)/Time
Perform the calculation.
Acceleration = (22 m/s – 4 m/s)/3 s = 18 m/s/3 s
Acceleration = 6 m/s2
The roller-coaster car’s average acceleration is 6 m/s2.
Calculating Acceleration

35. Graphing acceleration
S
P
E
E
D
T i m e
Object
accele-
rates
Object moves
at constant
speed
Object decelerates

36. Now You Try:
A roller coasters velocity at the top
of the hill is 10 m/s. Two seconds
later it reaches the bottom of the hill
with a velocity of 26 m/s. What is
the acceleration of the coaster?

37. The slanted, straight line on this speed-versus-time graph tells you that
the cyclist is accelerating at a constant rate. The slope of a speed-
versus-time graph tells you the object’s acceleration. Predicting How
would the slope of the graph change if the cyclist were accelerating at a
greater rate? At a lesser rate?

38. Since the slope is increasing, you can conclude that the
speed is also increasing. You are accelerating.
Distance-Versus-
Time Graph The
curved line on this
distance-versus-time
graph tells you that
the cyclist is
accelerating.

39. Acceleration Problems
A roller coaster is moving at 25 m/s at the
bottom of a hill. Three seconds later it reaches
the top of the hill moving at 10 m/s. What was
the acceleration of the coaster?
Initial Speed = 25 m/s
Final Speed = 10 m/s
Time = 3 seconds
Remember (final speed – initial speed) ÷ time is acceleration.
(10 m/s – 25 m/s) ÷ 3 s = -15 m/s ÷ 3 s = -5 m/s2
This roller coaster is decelerating.

40. A car’s velocity changes from 0 m/s to 30
m/s in 10 seconds. Calculate acceleration.
Final speed = 30 m/s
Initial speed = 0 m/s
Time = 10 s
Remember (final speed – initial speed) ÷ time is acceleration.
(30 m/s – 0 m/s) ÷ 10 s = 30 m/s ÷ 10 s = 3 m/s2

41. A satellite’s original velocity is 10,000 m/s.
After 60 seconds it s going 5,000 m/s. What
is the acceleration?
Remember (final speed – initial speed) ÷ time is acceleration.
Final speed (velocity) = 5000 m/s
Initial speed (velocity) = 10,000 m/s
Time = 60 seconds
(5000 m/s – 10,000 m/s) ÷ 60 s = -5000 m/s ÷ 60 s
= -83.33 m/s2
**This satellite is decelerating.

42. • If a speeding train hits the brakes and it
takes the train 39 seconds to go from 54.8
m/s to 12 m/s what is the acceleration?
Remember (final speed – initial speed) ÷ time is acceleration.
Final speed= 12 m/s
Initial speed= 54.8 m/s
Time = 39 s
12 m/s – 54.8 m/s ÷ 39 s = -42.8 m/s ÷ 39 s
= -1.097 m/s2
This train is decelerating.

43. A child drops a ball from a window. The ball
from drops strike the ground in 3.0 seconds.
What is the velocity of the ball before it hits the
ground?
Remember (final speed – initial speed) ÷ time is acceleration.
a= ∆v , ∆v=vf-vi
Since the ball is going against the gravity the acceleration will be(-9m/s2)
a=vf/t
-9=vf/30
Vf=-9(3.0)
=-27m/s

44. RELATION BETWEEN ACCELERATION AND NEWTON 2ND
LAW OF MOTION
The acceleration of the body is directly
proportional to the net force acting on the body
and inversely proportional to the mass of the
body. This means as the force acting upon an
object increases the acceleration of the object
increases

45. NEWTONS 2ND LAW
OF MOTION
• Once you have mass
and force , you can work
out acceleration of the
body
∑f=ma
Where f=force
m=mass
a=acceleration
This equation for
acceleration can be used to
calculate the acceleration
of an object when its mass
and the net force acting on
it are known

46. Problems for Newton’s Second Law
What force must act on a 50.0-kg mass to
give it an acceleration of 0.30 m/s2?
solution
F = m a= ( 50.0 kg )( 0.30 m/s2 )
15 kg m/s2= 15 newtons
= 15 N

47. A 1500-kg car starting from rest attains a speed of
25.0 m/s in 50.0 s.(a) What is the acceleration? (b) force
acting on it?
a) solution
a =(vf – vi)/t
=(25.0 – 0)/50
=0.5m/s2
b) solution
F = m a
( 1500 kg )( 0.50 m/s2 )
750 N

48. Momentum and newton 2nd law of motion

49. Problems on momentum
• 0.5kg ball moves at 2m/s. The ball is hit with force F
opposite to the ball direction , so the ball speed is
changed to 6m/s. The ball in contact with a hitter for
0.01 seconds. What is the change in momentum of
the ball
solution
∆p=mvf-mvi
=m(vf-vi)
=(0.5kg)(-6m/s—2m/s)
4kgm/s

50. a 10kg body is moving with a constant
acceleration of 4m/s2 .if the initial velocity of
the body is 2m/s , what is the change in
momentum in 5s
solution
f=ma ,(10kg)(4)
f=40N
since F=∆P/t , ∆p=F*t
=40N*5s
200kg.m/s