1. FA Quiz

2. A fly-by review of forces, inertia, and friction…

3. THE BIG IDEAS from the last class…
A force is a push or a pull
A force is measured in Newtons
Forces that are equal and opposite in direction are balanced.
Unbalanced forces cause changes in motion that can be predicted and described.

4. Inertia – IS NOT A FORCE tendency to resist any change in motion
property of all matter
tendency to resist any change in motion
object at rest, tends to remain at rest
object in motion, will keep moving at the same speed and in the same direction (same velocity)

5. Inertia greater the mass, the greater the inertia
direct or linear relationship to mass
greater the mass, the greater the inertia
greater the inertia, the larger the force needed to change its velocity

6. Which has greater mass – a bowling ball or a Ping-Pong ball?
Which has more?
Which has greater mass – a bowling ball or a Ping-Pong ball?

7. 2. Which has more inertia– a bowling ball or a Ping-Pong ball?

8. Which has more?
3. Which will require more force to change its motion – a bowling ball or a Ping-Pong ball?

9. A force that opposes motion between two surfaces that are in contact
Friction
A force that opposes motion between two surfaces that are in contact

10. Direction of Friction
Friction always points in the direction that resists motion
FRICTION

11. Two main types of friction
Static friction – occurs when a force is applied to an object but does not cause motion
Kinetic friction – Friction between moving surfaces

12. Three Kinds of Kinetic Friction
Sliding Friction – When solid surfaces slide over each other
Rolling Friction – When an object rolls over a surface
Fluid Friction – When an object moves through a fluid

13. How to Increase/Decrease Friction
Greater forces applied to the object increase friction

14. How to Increase/Decrease Friction
Rougher surfaces on the objects increases friction
VS.

15. How to Increase/Decrease Friction
The amount of area in contact does not affect friction

16. Air Resistance
Air resistance is a force that slow down objects that are moving through the air. Air resistance is caused by the collision of a solid object with gas molecules in the atmosphere.
The greater the surface area of the object, the greater air resistance
The shape of the object also determine how much air resistance is present
The faster an object is falling through air (its speed), the greater the air resistance

17. Friction – Helpful or Harmful?

18. How do Wheels reduce friction
Textbook
Plastic grocery bag
Spring scale
Rubber band
Pencils
Marbles
Directions
Put your textbook in a plastic grocery bag.
Hook the spring scale to the handles and pull the book across the table.
Read the measurement on the spring scale while the book is at a constant motion.
Record the measurement on the chart. Be sure to label all units.
Repeat steps 1-4 using the pencils and the marbles.
Put a rubber band around the book & the plastic grocery bag and repeat steps 1-4.
Data Table
Surface
Force
Book in a bag
Book on pencils
Book on marbles
Book with rubber band

19. Discuss Results What is friction?
Which object acts like wheels? Explain why.
 In which example was the force of friction the least? Explain.
In which example was the force of friction the greatest? Explain.
 List four ways friction is helpful in your life.