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