Newton’s Second Law of Motion You will be learning: 1.Newton’s Second Law of Motion. 2.Three types of friction. 3. The effects of air resistance on falling objects.

Newton’s Second Law of Motion Force = Mass x Acceleration or F = m x a F = ma

Force is always measured in Newtons (N) F= 20 kg x 20 m/s 2 = 400N m = F a = F a m

Friction Friction is the force that opposes the sliding motion of two surfaces that are touching each other. Remember that molecules and atoms have surfaces.

Microwelds – when two surfaces are in contact with each other the electrons start to join. Ex: file cabinet (When you first start to move it, it is very hard to move. Once it starts to move it is easier to move.)

Static Friction – when two surfaces are in contact and the friction prevents the two surfaces from sliding past one another Sliding Friction – the opposing motion when two surfaces are sliding across one another Rolling Friction – the friction between a rolling object and the surface it rolls on

Air Resistance Air Resistance opposes the motion of an object movement through the air Flat sheet of paper vs. balled up sheet of paper - Which will hit the ground first The purpose of a parachute.

Terminal Velocity When the upward air resistance force becomes large enough to balance the downward force of gravity In other words you have reached the fastest falling point you can reach.