# Newton’s 1 st and 3 rd Laws. How do you start and stop the motion of an object?

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Newton’s 1 st and 3 rd Laws

How do you start and stop the motion of an object?

Newton’s First Law If you know how to start and stop the motion of objects you know something about Newton’s First Law The Law states: An object at rest will remain at rest and an object in motion will remain in motion unless acted on by an unbalanced force Without an unbalanced force, a moving object will keep moving and an object at rest will remain motionless

What happens to your body when…..

Inertia The forward movement of your body is caused by inertia The brakes stop the car but not your body, so your body keeps moving forward Inertia is the tendency of an object to resist a change in motion

Inertia and Mass The inertia of an object depends on its mass Objects with greater mass have greater inertia To change the motion of an object, inertia must be overcome by an unbalanced force acting on the object

Newton’s 3 rd Law

Yesterday we talked about how to start and stop the motion of an object What did we say about how to start a skateboard? Why does the skateboard move in the opposite direction of the push from your foot?

Newton’s 3 rd Law The law states: Every action has an equal and opposite reaction Forces always act in pairs First an action occurs Pushing against the ground with your foot on a skateboard Then a reaction occurs The skateboard moves forward

Action and Reaction Forces The reaction force is always equal in strength to the action force but in the opposite direction Blue arrow = action force Green arrow = reaction force These forces can be represented with arrows Way arrow points = direction of force Size of arrow = strength of force

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