Friction and Gravity

1. What is friction?

The force that two surfaces exert on each other when they rub against each other.

Byproduct of friction…Heat!

2. What direction does friction act?

• Acts in direction opposite to the objects in motion.

3. How do you show friction as a force?• An arrow opposite of the object’s

motion

                                                     

              

Friction force

Motion

4. What determines the strength of friction?The types of surfaces (smooth or rough)

and how hard the surfaces push together

5. What are 4 types of friction?

a. Static friction: acts on object NOT moving:

b. Sliding FrictionTwo solid surfaces slide over each other

ex: pushing book across desk

ex: once the sled is moving, sliding friction

c. Rolling Friction

Object rolls across a surface

ex: ball bearings

d. Fluid Friction

• Solid object moves through a fluid

ex: oil, water, air

(what do you use in your car to reduce friction?)

• What are two ways in which friction can be useful?

• allows objects to remain in place!

• allows moving objects to stop to avoid colliding with other objects!

6. What is gravity?

• The force that pulls objects toward each other

                       

- Friction and Gravity

Universal Gravitation•Two factors affect the gravitational attraction between objects in the universe: mass and distance.

7. How do you show gravity as a force on Earth?• An arrow toward the center of Earth

Gravity

8. What is weight?

• The gravitational force exerted on an object

http://youtube.com/watch?v=L55jImEhNZ0

9. What is the acceleration due to Earth’s gravity?

• 9.8 m/s2

What is your weight (on Earth)?

Weight = Mass × 9.8 m/s2

Weight = ?

10. What is free fall?

• When the force of gravity alone causes an object to accelerate downward.

• Causes an object to accelerate downward at 9.8 m/s2

11. What is air resistance?• Type of fluid friction as an object

moves through air.

• Depends on speed and surface area

Air resistance

Free fall:

Gravity

Air resistance

Net Force

accelerate downward

Free fall:

Terminal velocity:

Gravity

Air resistance

0 net force

Move at constant

speed

Terminal velocity:

Gravity

Air resistance

Net Force

Gravity

Fluid friction

Gravity

Rolling friction

Air resistance