FORCES AND NEWTONS LAWS OF MOTION Preview n

FORCES AND NEWTON’S LAWS OF MOTION Preview

n 1 pound = 4. 45 Newtons 500 lb Elephant = 2, 225 N

Newton’s 1 st Law n n An object at rest remains at rest, and an object in motion remains moving at that velocity, unless a net external force causes the motion to change. We often refer to Newton’s first law as the law of inertia.

n n Inertia The tendency of an object to stay in motion , or resist change in motion mass is a measure of inertia

n BMW Inertia n Physics Force - U of Minnesota

Newton’s second law n

A student pushes a loaded sled whose mass is 240 kg for a distance of 2. 3 m over the frictionless surface of a frozen lake. He exerts a horizontal force equal to 130 N. If the sled starts from rest, what is its final velocity ?

Equilibrium n n n Equilibrium – a condition when the forces on an object are balanced. Static Equilibrium = an object at rest Dynamic Equilibrium = an object travels with constant velocity

Unbalanced Forces n Unbalanced forces accelerate an object

The Weight (Fg) of an object is defined as the amount of gravitational force acting on its mass. n n n F = ma becomes Fg= mg g = acceleration due to gravity g = 9. 8 m/s 2

n Normal Force (FN) n n A force exerted between 2 objects being squeezed together in a direction normal (or perpendicular), to surfaces in contact. Tension (FT) n Force exerted through string, rope, cord, chain, etc.

An elevator cable supports an empty elevator car of mass 300 kg. Determine the tension in the cable when the elevator car is (a) at rest and (b) the car has a downward acceleration of 2. 0 m/s 2. FT W n A) FT = W = mg = (300 kg)(10 m/s 2) = 3000 N. n B)