Describing Motion Newton’s Laws

First we need to define the word FORCE: A push or a pull exerted on an object in order to change the motion of the object.

Forces are measured in Newtons Symbol: N Measured by using a spring scale

Forces may be balanced or unbalanced Balanced forces – all forces acting on an object are equal –There is NO MOTION Unbalanced forces – one or more forces acting on an object are stronger than others –There is MOTION A NET FORCE

Friction Friction is a force that opposes motion between two surfaces that are in contact.

Types of Friction Kinetic Friction – sliding or rolling Static Friction - when a force is applied, but the object does not move

Newton’s Laws First Law – Inertia Second Law – Acceleration, Force & Mass Third Law – Action-Reaction

First Law Inertia –An object at rest [not moving] remains at rest unless acted on by a force [push or pull] –An object in motion remains in motion unless acted on by a force [push or pull]

First Law Inertia & Mass –Mass is the amount of matter in an object –The more MASS an object has, the more INERTIA the object has. –Bigger objects are harder to start & stop

Second Law –The acceleration of an object depends on the mass of the object and the amount of force applied –Formula: Force = mass x acceleration

Second Law Acceleration & Force –The more force placed on an object, the more it will accelerate [change its motion] Acceleration & Mass –The more mass [or inertia] an object has, the more force it takes to accelerate the object

Third Law Action – Reaction Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.

The truck is in motion. What is the force that causes it to stop? The push of the stopped car. The car is at rest. What is the force that causes it to move? The push of the truck.

What about the ladder on top of the truck? The ladder is in motion because the truck is in motion. When the truck stops, the ladder stays in motion. The truck is stopped by the force of the car, but the ladder is not. What force stops the ladder? Gravity.

The truck is in motion, the car is at rest. How do each of these vehicles accelerate? The truck stops moving. The car starts moving. Which one will be the hardest to accelerate? The truck because it has the most mass.

Why does the car move [accelerate] when it is hit by the truck? The heavy and moving truck has more force than the small, at rest car. Why does the truck stop moving when it hits the car? The force of the car pushing back on the truck, plus the force of friction between the massive truck and the road slow down, the stop the truck.

The truck hits the car. An action force stops the truck. What is the equal and opposite reaction force? The force that pushes the car forward.