1. Force

2. Review Describing Motion
•Speed - How fast?
•Time- How long?
•Distance- How far?
•Velocity- How fast in a direction
•Acceleration - How fast “how fast” is changing?

3. Forces Pushes or pulls May cause acceleration [changes in motion]
May also cause changes in shape

4. Balanced Forces All forces acting on an object are equal
There is no motion

5. Unbalanced Forces All forces acting on an object are not equal
One or more force is stronger than others
Motion occurs

6. Net Force The sum of all forces acting on an object A net force of 0
No motion
A net force of more than 0
Motion occurs

7. Combining Forces =
5 N
10 N
5 N =
5 N
10 N
5 N =
5 N
5 N

8. What is friction? Friction force that opposes the motion of an object
the force of friction works in the opposite direction of the force of motion

9. Types of Friction Sliding Friction (Kinectic)
the source of friction is the contact between two surfaces, at least one of which is in motion

10. Types of Friction Air Resistance
friction results from air pushing on an object as it is moving

11. Types of Friction Rolling Friction
friction between two surfaces that are not in constant contact
ex. wheels

12. Types of Friction Static Friction
Force applied by object does not move
Forces are balanced
Takes greater force to move
Disappears as soon as an object starts moving

13. Friction friction makes motion possible
friction also makes it hard to move objects
reducing friction makes it easier to move objects

14. How can friction be reduced?
by changing sliding friction into rolling friction
by using lubricants
Lubricants – substances that reduce friction

15. Gravity Force that attracts all objects toward each other
More mass = more gravity
Acceleration because of gravity is 9.8 m/s/s
All objects accelerate at the same rate