Newton's Laws

​What we will cover

• definitions of the 3 laws

• real life examples ​

• sample questions ​

​Balanced and Unbalanced Forces

• ​A force is a push, pull, or twist - that results in the changing shape or movement of an object

• Forces can be balanced or unbalanced. Unbalanced forces will result in motion or a change in direction or speed.

• Measured in Newtons (N)​

​1st Law

​An object at rest will stay at rest and an object in motion will stay in motion, unless acted upon by an unbalanced force

​Another name for this law is inertia.

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​Inertia = the resistance of any object (with mass) to change its velocity.

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Example: ​if a bus stops suddenly, you lurch forward, even though the bus is no longer in motion

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​Examples:

• ​Ball rolling on the ground (friction will eventually stop it)

• ​Brakes being applied in a car

• ​Fan continuing to move even after it is powered off

• An object skating on ice ​

​2nd Law

​The acceleration of an object is proportional to the magnitude of the net force, and is inversely proportional to the mass of the object.

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OR

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Force = mass x acceleration

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This makes logical sense, because the more mass an object has, ​the more force required to move it. Or, the more an object accelerates, the more force required to move it.

​Example question:

​How much force is required to accelerate a 2kg mass at 3m/s²?

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force = mass x acceleration

force = 2 x 3

force = 6 N​

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How much force is required to accelerate a 10kg mass at 3m/s²?

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Force = 10 x 3

force = 30 N​

​Newton's 3rd Law

​For every action there is an equal and opposite reaction.

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Every force is in a pair:

• ​a swimmer propelling themselves through the water with their hands. The hands and the water are exerting an equal but opposite force direction on each other.

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This does not mean they are balanced (and therefore cancel each other out), they are acting on different objects. ​

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