2. What is the net force?
Draw a free body diagram for the car.
40N
60 N

3. A force between two surfaces that opposes motion
Friction:
A force between two surfaces that opposes motion
FRICTION
Science of the Olympics

4. Friction
What stops a ball from rolling across the room forever and ever?
The force is called FRICTION.
Friction is a force that opposes motion between two surfaces that are in contact.

5. Friction Friction occurs because the surface of any object is rough.
All surfaces are filled with microscopic hills and valleys that make them rough.
The heavier the object the more force that is exerted on the object and more friction.
velcro

6. Different Surfaces Cause different amounts of Friction
Ice: Low Friction
Gravel Road: High Friction

7. FRICTION
Motion

8. Check for Understanding
Which would have more friction a 2lb book or a 5lb book?
Why do objects slow down when moving?

9. Categories of Friction
Kinetic Friction
Moving
Static Friction
Stationary

10. Static Friction
Static friction is the friction of an object that is not moving.
The object does not move because the force of static friction balances the applied force
If you were to get up and push the wall would it move? Why not?

11. Static Friction
Friction
Friction cancels out the force on the object and the object does not move!

12. Kinetic Friction Kinetic Friction is moving friction.
For example rolling or pushing an object produces kinetic friction.
Do you think its easier to push a chair or roll it? Which would have more friction?

13. Kinetic Friction
Motion
FORCE OF
FRICTION f
Pull

14. Sliding Friction Two solid surfaces slide over each other Examples
spreading sand on an icy path
Brakes pads on a bicycle
Sledding down a hill
Falling off of the bicycle and skinning your knee.

15. Rolling Friction
Friction that occurs when an object rolling across a surface
Easier to overcome than sliding friction
Ex: skates, skateboards, cars, bicycles… anything with a tire using the wheels to move freely

16. Fluid Friction Friction that occurs when an object moves fluid aside
Easier to overcome than sliding friction
can be called air resistance or drag
Fluid friction occurs between you and the air
It can be reduced by streamlining

17. > Static Friction Kinetic Friction
Static Friction is always Greater than Kinetic Friction

18. Friction is Helpful

19. Friction, (Ff) depends on only two things:
The type of surface (ice, cement, etc…)
The mass of the object

20. Also… Friction turns work into heat energy
In every energy transformation, some energy is “lost” as heat due to friction

21. Gravity

22. Gravitational Force is a force of attraction between objects
ALL objects with mass exert a force of gravity on ALL other things
“discovered” by Isaac Newton
Gravity on Earth has a acceleration of 9.8 meters per second squared

23. Gravitational Force Diagrams
If the mass of either of the objects increases, the gravitational force between them increases.
If the distance between the two objects increases, the gravitational force between them decreases.

24. Brain Pop Gravity
What 2 factors affect how strong the force of gravity is between 2 objects?

25. MASS and DISTANCE Family Guy Big Bang (2:54-3:30)
Gravity depends on 2 things:
MASS and DISTANCE
Family Guy
Big Bang (2:54-3:30)

26. The Rules of Gravity
Gravitational force increases as the mass of objects increases.
More massive object exerts more gravity
Gravitational force increases as distance between 2 objects decreases.
Closer together = more gravity
3rd rule: Gravity pulls from all sides at the same rate.
-why planets and stars are round.

29. 3rd rule: Gravity pulls from all sides at the same rate
3rd rule: Gravity pulls from all sides at the same rate. -why planets and stars are round.

30. Mass vs. Weight
Weight measures the gravitational force on an object’s mass.
Weight changes when gravity changes
Measured in newtons (N) with a scale
Mass measures the amount of matter in an object
Does NOT change with gravity
Measured in kilograms (kg) with a triple-beam balance

32. http://www.youtube.com/watch?v=xfGll1REu 2A

33. Objects fall to the ground at the same rate because the acceleration due to gravity is the same for all objects
9.8 m/s2 on Earth

34. Air resistance (fluid friction) is a force that acts to slow falling objects; results from upward force of air molecules, opposing gravity

35. Terminal Velocity
The greatest velocity a falling object reaches is its terminal velocity
Net force = 0 N
object stops accelerating and travels at constant speed
drag+buoyant force = gravity