FORCEDefinition:

A push or a pull Force can cause motion

SI unit -> Newton (N)= 1 kg x 1 m/s2

Sometimes pound (lb) can be used as a unit for force

1 Newton=0.22481 pounds force

COMBINING FORCES

B. Balanced Force Equal and opposite forces = ‘balanced’ Balanced forces give no motion

No motion of hands

COMBINING FORCES Unbalanced force – more force in one direction (net

force)

NET FORCE

Bigger force to the right Smaller force to the left Net force to the right

III. FRICTION AND GRAVITY

A. Friction – a force that opposes motion

1. Caused by the interaction between two touching surfaces rubbing against each other

2. Four Types

A. STATIC

Friction that acts on something that is not moving

No heat or wear is generated

B. SLIDING

Force resulting when pushing or pulling an object over a surface.

C. ROLLING

Contact is reduced because of rollers or wheels or ball bearings.

D. FLUID FRICTION

Resistance from a “fluid” Fluids are liquids and gases.

REDUCING FRICTION

A smooth surface does not demonstrate as much friction as a rough surface.

Waxing, oiling, etc. can be used to reduce friction.

COEFFICIENT OF FRICTION

µ= “coefficient of friction” represents the roughness of the surfaces in contact.

In reality there two main subtypes:

1. µs - Static friction to get it moving2. µk- Kinetic friction to keep it moving  µs > µk needed for movement to occur

B. Gravity – force of attraction between two objects---> pulling force

Factors Affecting Gravitya. Mass – more mass, more gravityb. Distance – closer, more gravity

http://www.exploratorium.edu/ronh/weight/

END CHECK- COMPLETE ON SEPARATE SHEET OF PAPER

1. Describe three ways in which a car’s velocity will change

2. Identify a one situation involving unbalanced force and one situation involving balanced force. Explain how it each affect the motion of an object.

3. Arrange the following pairs of surfaces in order of most friction to least friction A shoe sole and a waxed basketball court A shoe sole and the frozen surface of a lake A shoe sole and the sidewalk

END CHECK- COMPLETE ON SEPARATE SHEET OF PAPER

4. Explain why Venus, which is slightly less massive than Earth, experiences a stronger gravitational pull from the sun than Earth does.

5. What is the average acceleration of a scooter that starts at rest and moves straight ahead at 12 m/s in 24 s.

6. Which will be moving faster after 3.0 s, a cyclist maintaining a constant velocity of 15 m/s straight ahead or a race car accelerating forward from a stoplight at 4.0 m/s2?