Newton’s Laws of Motion



Newton’s Laws of Motion

Newton’s First Law of Motion

Newton’s first law of motion says that an object at rest will stay at rest unless acted on by an unbalanced force. This means that an object will not start moving until a push or pull is exerted on it. This happens because of Inertia. (Ex. Golf club hitting ball: See Figure 11 p. 145 of text)

Newton’s first law of motion also says that an object moving at a certain velocity will continue to move that the same speed and in the same directions forever unless another force acts on it. This happens because of Inertia.

Friction makes it hard to see the effects of Newton’s first law in action. For example, a ball rolling on grass will slow down and stop because of the friction between the grass and the ball. It will not go on moving forever because of friction

Inertia is the tendency of all objects to resist any change in motion. Inertia is what makes you slide toward the side of the car when the driver makes a turn.

An object with small mass has less inertia than an object with a large mass. It is easier to start and change motion of an object with small mass.

Ex: Inertia makes it harder to push a car than to push a bicycle because the car has more mass than the bike. (See Figure 13 on p. 147 of textbook)

Newton’s Second Law of Motion

An object’s acceleration decreases when its mass increases. An object’s acceleration increases when its mass decreases.

Example: An empty shopping cart will accelerate with only a small amount of force applied. A full shopping cart (with more mass) will not accelerate as much with the same amount of force applied. (See Figure 14, p. 148 of textbook)

The more force put on an object, the greater the acceleration. The less force put on an object, the less the acceleration.

Newton’s Third Law of Motion

All forces act in pairs. There is an action force and a reaction force. The two forces are equal in size but are in opposite directions.

Example: Look at the picture of the swimmer below. The action force is the swimmer’s hands & feet pushing on the water. The reaction force is the water pushing on the hands and feet. This moves the swimmer forward.

Other Examples of Newton’s 3rd Law in Action

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An object at rest remains at rest and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force.

Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

The acceleration of an object depends on the mass of the object and the amount of force applied.

The shuttle’s thrusters push the gas down and the gases push the shuttle up.

The bat exerts a force on the ball. The ball exerts an equal force on the bat, but in the opposite direction.

The rabbit’s legs exert a force on the ground. The ground exerts an equal force on the rabbit’s legs. This causes the rabbit to jump up.

Newton’s 1st Law

How does Newton’s 1st Law affects objects at rest?

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How does Newton’s 1st Law affects object that are in motion?

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Inertia is ___________________________________________________

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Which has more inertia, a car or a bicycle? _________________________

Newton’s 2st Law

If the mass of an object gets bigger, will the acceleration of that object increase or decrease? ______________________________

Why is it harder to push a full shopping cart than an empty one?

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Newton’s 3st Law

Tell how Newton’s 3rd Law affects a swimmer swimming through water. (Talk about the action force and the reaction force!)

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Give 1 real life example of Newton’s 3rd Law in action:

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