Force and motion

What causes an object to move?
 A FORCE!
 ALL motion is due to forces acting on
objects!
What is a force?
 A push or a pull
MOTION

Motion
 What is motion?
 A change in the position of an
object over time.
 How do you know something
has moved?
 You use a reference point!
 A stationary (not moving) object
such as a tree, street sign, or a
line on the road.
Did the
beaver
move?

Can more than
one force act on
an object at the
same time?
#2
#3
#1
YES!
Example: Gravity is pulling
you down to Earth, the
ground is supporting
you, and your legs
moving you forward as
you run during PE.
The total combination of the
forces acting on an object is
called NET FORCE.

Balanced Forces
 A balanced force is one in which the net force
equals ZERO.
 Do you think there will be any motion?
 NO!
 Examples:
25 Newtons 25 Newtons

Unbalanced Forces
 An unbalanced force is one in which the net
force is greater than zero.
 Do you think there will be any motion?
 YES!
 Examples:
25 Newtons 40 Newtons 2 N
50
N

Only an _______________
force can change the motion
of an object.
Example: Your
doggy can cause
you to move if he
pulls with enough
force.
 His force is greater than
the force you’re using to
stay in place

What would happen if an
unbalanced force acted on an
object that’s already in motion?
 It will change the speed
or direction of the
object.
 Example: Your sisther is
driving her car. You run
up behind her and give
her a push.
 Your force adds to the
existing force causing
her to speed up.

Unbalanced forces can act
in the same direction.
 Example: You’re pushing a cabinet across the room
with a force of 15 N. You’re friend is pulling with a
force of 10 N.
 What is the NET FORCE?
 What direction is the cabinet moving?
15 Newtons 10 Newtons

Unbalanced forces can act
in opposite directions.
 Example: Six people are tugging on a rope.
Three people pulls with a force of 20N and
the other pulls with a force of 25N.
 What is the NET FORCE?
 What direction is the rope moving?
25 Newtons20 Newtons

Friction and Gravity
 What is friction?
 A force that opposes the motion of an object
 It’s a “contact” force!
 Occurs when an object in motion rubs against a surface.
 The contact reduces the speed of the object and
releases heat.

What affects the
amount of friction?
 The force of the
push/pull
 The harder you push, the
longer it’s going to take
friction to stop the
object.
 The bumpiness of the
surface
 The rougher the surface,
the more friction.
 The weight of the
object
 The heavier the object,
the more friction.

 What is gravity?
 The force of attraction between all objects.
 The amount of gravity depends on two things:
 The objects’ masses
 The distance between the two objects

 Since the earth is so large,
everything on it is attracted
to it even if they’re not
touching!
 Example: Apple fall
 Apple fall because the gravity
of the earth.

1. What is the net force on the box shown below?
a)10 N to the left
b) 10 N to the right
c) 60 N to the left
d) 50 N to the right
10 N
10 N
10 N
Questions
Choose the correct item.

2 .Which force always pulls downward on objects?
a) Support force
b) Friction force
c) Gravity
d) Air resistance

3.A force is described as...
a) A push only
b) A pull only
c) A push or a pull
d) None of the above

4. A change to an objects motion is caused by...
a) Balanced forces
b) Unbalanced forces
c) Acceleration
d) Velocity

5.Describe the motion of a person not wearing a seat
belt if the car stops suddenly.
a) The person and car will stop together.
b) The person will stop faster than the car because they are
lighter.
c) The car will stop and the person will keep moving
forward because of inertia.
d) The car will stop and the person will speed up.

6.A falling object is pulled down by the earth. The earth
is pulled up toward the object. Why doesn’t the earth
move?
a) Only the earth has gravity.
b) The Earth has a very large mass and a small
acceleration.
c) The Earth has a very small mass and a large
acceleration.
d) Air resistance gets in the way.

7.What forces are acting on a dropped book that falls to
the floor?
a) Gravity only
b) Gravity and air resistance
c) Air resistance
d) Friction only

8.Which ball will hit the ground first?
wood ball Plastic ball metal ball
a) Metal first, then plastic, then wood last
b) Wood first , then plastic, then metal last
c) They will all hit at the same time.
d)There is no way to tell.

9. A duck flies 60 meters in 10 seconds. What is the
duck’s speed?
a) 600 m/s
b) 50 m/s
c) 6 m/s
d) 70 m/s

9. A duck flies 60 meters in 10 seconds. What is the
speed?
a) 600 m/s
b) 50 m/s
c) 6 m/s
d) 70 m/s

10.What unit do scientists use to measure force?
a) Newton
b) Grams
c) Meters
d) Meter per second per second

11.This test paper is sitting at rest on your desk. Which of
the following statements best describes this situation?
a)There are no forces acting on your paper.
b)Your paper pushes on the desk only.
c)The desk pushes on your paper only
d)The forces acting on the paper are balanced.

12. A beetle crawls 2 cm/minute for ten minutes. How
far did it crawl?
a) 8 centimeters
b) 5 centimeters
c) 2 centimeters
d) 20 centimeters

13.When you slide a box across the floor what force must
your push be stronger than?
a) Support force
b) Friction force
c) Gravity
d) Air resistance

14.The moon has a smaller mass than the Earth. If you
were able to travel to the moon your weight would...
a) Increase
b) Decrease
c) Stay the same
d) Vary with day and night

Group Force
 Mr.Weerachat Martluplao
 Miss.Mookda Bannabuppha
 Mrs.Ganyarath Prommakoon
Workshop Science and Match Teaching Training in
Engilish Program

Force and motion

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