1. Forces Georgia Performance Standards
SPS8. Students will determine relationships among force, mass, and motion.
b. Apply Newton’s three laws to everyday situations by explaining the following:
Inertia
Relationship between force, mass and acceleration
Equal and opposite forces
c. Relate falling objects to gravitational force
d. Explain the difference in mass and weight.

2. Definition: A push or a pull
Force
What comes to mind?
Definition: A push or a pull
Gives energy to an object, sometimes
causing it to start moving, stop moving or
change direction.

3. Examples Magnet pulling iron Wind pushing a door Throwing a baseball
What are some other examples

4. Total (Net) Force Acts in a particular direction
Vector- shows magnitude and direction
Force is a VECTOR.
When 2 forces are exerted in the same direction, they ADD together.
When 2 forces act in OPPOSITE directions,
they combine by SUBTRACTION
Force is measured in newtons.
1 Newton = 1 kg-m/s2

5. Balanced Forces
forces that are in opposite directions and are equal in size.
40 N
40 N
No change in motion,
TOTAL (net) FORCE = 0 N Why?
60 N
60 N

6. Unbalanced Forces
when TOTAL (net) force of an object is in 1 direction
Movement is in which direction?
100 N
20 N
100 N
Total (Resultant) Force? _________
20 N
Total (Resultant) Force? ______

7. Real life examples What are some other examples?
What are some other examples?

8. Friction Is a Force that acts opposite to the motion.
Causes a moving object to slow and/or stop.
Rough surfaces have more friction than smooth surfaces
What are some examples of friction?

9. 4 Types of Friction
Greatest
Friction
Static Friction– friction between objects that are NOT moving.
Sliding Friction– friction between solid objects (at least one is moving)
Rolling Friction– friction produced by moving wheels on a solid object
Fluid Friction– force exerted by fluids (gases or liquids) (such as air, water or oil)
Least
Friction

10. Static Friction Examples…. The friction between these objects and the
floor that you
have to overcome
to move them.

11. Sliding Friction
Example…
What are some other examples?

12. Rolling Friction
Examples…
What are some other examples?

13. Fluid Friction Examples… What are some other examples?

14. Benefits of Friction Wheels to road in car allows car to stop.
Brake system in car.
Walking… shoes to ground.
Causes Heat (in body) (shiver)
Other Examples?

15. Problems with Friction
Friction causes heat. (in machines)
Lubricant (oil, wax or
greases) – changes
sliding friction
to fluid friction.
(lessening frictional
force!!)

16. Newton’s 3 Laws of Motion
1st Law… aka Inertial Law
A body in motion will stay in motion at a constant velocity unless acted upon by an outside force
Inertia –the tendency of a body at rest to stay at rest or a body in motion to stay in motion

17. 2nd Law… (net) Force = mass X acceleration
OR acceleration = (net) force / mass
What if the Net force is zero? How much will a body accelerate? a = 0 N /500 kg
So for a body to accelerate there must be a net force (however small)

18. 3rd Law… For every action, there is an equal and opposite reaction
Forces act in pairs * action/reaction law

19. Forces
Any Questions?