Describing Motion Newton’s Laws

First we need to define the word FORCE: There are two types of forces Unbalanced forces cause objects to accelerate Forces occur when objects interact with each other

Action-at-a-Distance Forces 2 Main Categories Contact Forces Friction Tension Normal Force Air Resistance Applied Force Spring Force Action-at-a-Distance Forces Gravity Magnets Electricity Strong (nuclear) Force

Forces are Represented by Arrows The head of the arrow shows the direction of the force The width of the arrow shows the strength of the force Large force pushing right Small force pushing left

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

Forces are measured in Newtons SI unit of force Symbol: N Measured by using a spring scale

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

First Law - Inertia An object at rest remains at rest unless acted on by an outside force. An object in motion remains in motion unless acted on by an outside force.

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 Acceleration & Mass Definitions Acceleration is a change in velocity [speed or direction] Mass is the amount of matter in an object

Second Law Acceleration & Force Acceleration & Mass 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

Calculate Newton’s Second Law Force = Mass x Acceleration F = m a

Third Law Action – Reaction Forces are always produced in pairs with opposite directions & equal strengths For every force there is an equal and opposite force

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 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.