# What causes motion?.

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What causes motion?

Sir Issac Newton Developed laws of motion by age 24.

Newton’s 1st Law of Motion
Law of Inertia A body at rest, stays at rest; a body in motion stays in motion until an outside force acts upon it. Demo: Flask, coin (or nut, screw), index card. Place the index card on top of the flask. Place the coin on the card. Make sure the coin will fit through the opening of the flask. Quickly flick the index card out, causing the coin to drop into the flask. You may need to practice. Repeat but this time move the flask slowly. The coin should stay on the card.

Inertia Tendency of an object at rest to stay at rest, or an object in motion to stay in motion.

Inertia All objects resist changes in motion.
All objects have mass, therefore they have inertia. An object with a small mass can be accelerated with a small force. Mass is a measure of inertia. Inertia is why cars, bikes, or planes do not stop instantaneously. If students have not been exposed to the concept of mass, explain it here. Review, if needed.

Newton’s 2nd Law of Motion
The acceleration of an object is directly proportional to the force acted upon the object and inversely proportional to the mass of the object.

Newton’s 2nd Law of Motion
If the Force increases, the acceleration of the object increases. If the mass is increased, the acceleration of the object decreases. a=F/m Using the abbreviation cards on the word wall, rearrange the formula for the different variables- Force and mass.

What is the acceleration of a 132 kg object being moved with a 268 N force?
m=132 kg F=268 N a=F/m a=268 N/132 kg a=2.03 m/s2

Force of gravity on an object Mass X Gravity (freefall acceleration)
Weight Force of gravity on an object Mass X Gravity (freefall acceleration) W = mg Stress that weight and mass are not the same thing! Since weight is a force, this is the same as Newton’s 2nd law of motion (F=ma).

What is the weight of Mark on Earth if his mass is 72-kg?
m=72 kg a=9.8 m/s2 W=mg W= (72 kg)(9.8 m/s2) W=710 N Example using the guidelines from the Math Checklist (lesson 1).

Newton’s 3rd Law of Motion
For every action, there is an equal and opposite reaction. Law of Action and Reaction

Action-Reaction Forces always occur in pairs.
Whenever a force is exerted, another force occurs that is equal in size an opposite in direction. Foot exerts a force on the ball (action); the ball exerts a force on the foot (reaction).