 # Newton’s 2 nd Law. Force on Object Objects acted on by a net unbalanced force will accelerate in the direction of the force This means they will speed.

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Newton’s 2 nd Law

Force on Object Objects acted on by a net unbalanced force will accelerate in the direction of the force This means they will speed up, slow down, or change direction

Newton’s 2 nd Law The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to the mass. The direction of acceleration is the same as the direction of the force a = ∑F / m ∑F = ma

Force Redefined Force can be redefined as an action capable of accelerating an object Unit of force is the Newton (N) One Newton is the force needed to accelerate a 1 kg mass at 1 m/s 2 1 N = 1 kg m/s 2

Examples What force is needed to accelerate a 1000kg car at ½ g? What is the net force required to bring a 1500 kg car to rest from 100 km/hr within a distance of 55 m?

A 50 kg go-cart starts from rest and is accelerated by a 550 N force. If the cart experiences a 280 N friction force and 35 N of air resistance, find a) it’s acceleration b) it’s velocity after 3.0 s c) its displacement after 3.0 s

What force must be exerted on a 500 kg crate in order to move it from rest to 3.0 m/s in 1.0 s?

If we apply Newton’s 2 nd Law to objects accelerating due to gravity F G = mg F G – force of gravity, commonly called weight W = mg 2 nd Law and Gravity

When an object is resting on the surface of Earth, the force of gravity is still acting, even though the object is not moving When the contact force acts perpendicular to the surface it is referred to as the Normal Force (F N ) Normal

A 10.0kg box is resting on a table a) draw the free body diagram b) now it is pushed down with a force of 40N. Draw the free body diagram. c) now it is pulled up with a force of 40N. Draw the free body diagram. Ex

A 3.5kg box is resting on the floor. Draw the free body diagram Example

What happens when the box in the previous problem is pulled up with a force of 100N? Ex.

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