Chapter 4 Newtons Second Law of Motion Newtons

Chapter 4 Newton’s Second Law of Motion

Newton’s Laws The nd 2 Law The Sum of the Forces acting on a body is proportional to the acceleration that the body experiences SF a S F = (mass) a

nd 2 2. NEWTON'S LAW OF MOTION F a m F M a m m F m a F M a

• If the net force is perpendicular to the velocity, the direction of the velocity changes. • Acceleration is always in the direction of the net force.

Units of Force • From the law SF = ma, we get Force = (kg)(m/s 2) = newton or Force = (slug)(ft/s 2) = pound

Dynamic Equilibrium Velocity is nonzero and constant Examples: Force from road Driving at constant velocity Normal up Friction Weight down

Oppose motion or the tendency of motion • Friction • Air Resistance

• Depends upon. . . – Materials that are in contact – Forces that press surfaces together (Normal forces) • Static friction (no motion) – Proportional to force used until maximum is reached • Kinetic friction (motion) – Nearly constant for normal speeds

Cause of Friction • Friction is caused by the “microscopic” interactions between the two surfaces

Friction Static F Kinetic f f F

Friction Measured • Force meter

Air Resistance • Depends on – Surface Area – Velocity • When weight = air resistance we have SF= 0 Þ a = 0 Terminal Velocity! Weight Air Resistance