A force is a push or pull between objects that has both size and direction. The net force on an object is the sum of all individual forces acting on it. Forces in the same direction are added, while forces in opposite directions are subtracted. Balanced forces produce no acceleration, while unbalanced forces cause acceleration that can be predicted using Newton's Second Law, which states that force equals mass times acceleration (F=ma).

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