Newton’s Second Law of Motion Chapter 4 Newton’s Second Law of Motion

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

2. NEWTON'S 2nd LAW OF MOTION

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 Force = (kg)(m/s2) = newton or From the law SF = ma, we get Force = (kg)(m/s2) = newton or Force = (slug)(ft/s2) = pound

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

Oppose motion or the tendency of motion Dissipative Forces Oppose motion or the tendency of motion Friction Air Resistance

Friction Depends upon... Static friction (no motion) 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 f Kinetic f F

Friction Measured Force meter

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