1. Forces

2. What is a force?
 A force is a push or pull from one
object to another object
 Examples: Earth’s gravitational pull on
us, you pushing a chair, a table
supporting a book

3. What is a force?
 All forces have both size and direction
 The unit of force is the Newton (N)
 What other concepts have both a size
and direction?

4. Net Forces
 The net force is the combination all of
the forces acting on the object
 Whenever more than one force act on
an object, always sum the forces into
a single net force

5. Forces in the Same Direction
 When forces act in the same direction,
you add the forces together
 The net force will be in the same
direction as the two original forces
F1= 5 N Fnet= 8 N
F2= 3 N

6. Forces in the Opposite Direction
 When two forces act in opposite
directions, you subtract the smaller
force from the larger force
 The net force will be in the direction of
the larger force
F1= 2 N F2= 7 N Fnet= 5 N

7. Balanced Forces
 When the sum of the forces acting on
an object equals zero, the forces are
said to be balanced.
 Balanced forces are equal in size and
opposite in direction

8. Balanced Forces- Newton’s 1st
Law
 There is no change in motion when
the forces are balanced.
 A stationary object remains stationary
 A moving object has constant velocity

9. Unbalanced Forces
 When the sum of the forces are non-
zero, there are unbalanced forces
acting on the object
 Unbalanced forces produce a change
in motion, so they are necessary to
cause accelerated motion

10. The Big Idea
 Unbalanced forces result in a net force
 The net force causes the object to
accelerate
 This acceleration can be predicted
and described

11. Force, Mass, and
Acceleration
 An object accelerates when a net
force acts upon it
 The net force is equal to the mass
times the acceleration:
F = ma
 This relationship is Newton’s 2nd Law

12. Force, Mass, and
Acceleration
 The acceleration of the object
depends on both the forces acting on
the object and the mass of the object
 The net force and acceleration are
always in the same direction!!
F1= 2 N F2= 7 N Fnet= 5 N
a

13. Example 1
 How much force is needed to
accelerate a 30 kg scooter at a rate of
1 m/s2?
F = ma
F = (30 kg) x
(1m/s2)
F = 30 N

14. Example 2
 How much force is needed to
accelerate a 0.5 kg baseball at a rate
of 0.04 m/s2?
F = ma
F = (0.5 kg) x (0.04
m/s2)
F = 0.2 N