Forces

Friction & Gravity

Chapter 2

Section 3

Friction

• The force that resists motion

• Smooth or rough?• How hard are the

objects pushed together?

Friction

• Good Things– Gives shoes traction– Let’s you strike a match

• Bad Things– Slows your bike down– Makes cars less efficient

Sliding Friction

• 1 object slides over another– Skiing

Rolling Friction

• 1 object rolls over another object– Train tracks

Fluid Friction

• Objects move through a fluid– “A well oiled machine”

• Better than sliding

Gravity

• The force that pulls objects to earth

Free Fall

• Maximum acceleration– No air resistance

Terminal Velocity

• F gravity = F air resistance • Maximum falling speed

Air Resistance

• Fluid Friction– Objects moving through air

Projectile Motion

• When an object is thrown horizontally– Forms a parabola

Weight

• Force of gravity on your body– Earth Gravity = 9.8 m/s2

– Moon Gravity = 1.6 m/s2

• 1/6 on the moon– Mr. Cady = 28 lbs.

Law of Universal Gravitation

• All objects in the universe are attracted to one another

• Stronger when…– Bigger– Closer