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NEWTON'S LAWS OF MOTION 2nd Law 1st Law 3rd Law

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**People DO NOT create laws governing the natural world.**

We only identify the principles that exist in the physical world and name them for reference!!

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**What makes objects move?**

What makes them change their motion?

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**Force Force – a push or a pull**

Contact Force – when 2 objects must be touching to exert forces on each other Friction Pushing or kicking a ball Long-Range Force – a force that is exerted without the objects having to touch Gravity Magnetism Nuclear force

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COMBINING FORCES Net force – combination of all forces acting on an object Balanced Forces – 2 or more forces acting on an object cancel each other – they do NOT change the motion of the object (Net Force = 0) Unbalanced Forces –forces acting on an object do NOT cancel each other – they DO change the motion of the object (Net Force ≠ 0)

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balanced force

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REST MOTION UNBALANCED FORCES

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REST The state of an object when it is not changing position. THIS IS RELATIVE!! Not moving in relation to your immediate surroundings!!!

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**MOTION THIS IS RELATIVE, TOO!!**

The state of an object when it is changing position in relation to its surroundings. THIS IS RELATIVE, TOO!! When you are sitting on an airplane, you are at rest, but if you get up and walk down the aisle, you are in motion.

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**If you are sitting in a seat on a speeding airplane you would still be considered at rest!**

If rest were defined as a total absence of motion, it would not exist in nature.

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**If an object is at REST, it takes an unbalanced force to make it move.**

UNBALANCED FORCES If an object is at REST, it takes an unbalanced force to make it move. If an object is in MOTION, it takes an unbalanced force to stop it, change its direction from a straight line path, or alter its speed.

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**ANY CHANGE IN AN OBJECT'S**

ACCELERATION ANY CHANGE IN AN OBJECT'S SPEED OR DIRECTION

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**There is no change in motion therefore no acceleration**

Balanced Forces There is no change in motion therefore no acceleration Unbalanced Forces There is a force pushing the book to the RIGHT that is GREATER than the force of FRICTION therefore there is acceleration.

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**Newton’s 1st Law of Motion**

INERTIA Lazy, resistant to change!!!

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**Newton’s 1st Law of Motion**

If there is NO net force acting on an object then An object at rest will remain at rest An object in motion will remain in motion at constant speed. Until acted upon by an outside force The truck stops when it hits the car, the ladder continues moving forward because the force of the car was acting on the truck NOT the ladder.

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**Newton’s 1st Law of Motion**

From a standing start the truck moves away very quickly causing the passenger to fall backward After traveling at some speed the truck suddenly comes to a stop causing the passenger to fall forward. Force was applied to the truck not the passenger!!!

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**Newton’s 1st Law of Motion**

MASS OF AN OBJECT = INERTIA OF AN OBJECT Less mass = less inertia (smaller resistance to change) More mass = more inertia (greater resistance to change)

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**Newton’s 1st Law of Motion**

MASS OF AN OBJECT = INERTIA OF AN OBJECT INERTIA of an object explains why a magician can pull the tablecloth out from under a set of glasses without having them fall over The glasses have more inertia than the tablecloth as the force (pull) is applied to the tablecloth.

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**Newton’s 2nd Law of Motion**

Force is equal to mass times acceleration F = ma

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**Newton’s 2nd Law of Motion**

Cannon

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**Newton’s 2nd Law of Motion**

When the cannon is fired, an explosion propels a cannon ball out the open end of the barrel. It flies to its target. At the same time, the cannon itself is pushed backward a meter or two. ACTION - work What happens to the cannon and the ball is determined by Newton’s 2nd Law.

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**m(cannon) a(cannon) = m(ball) a(ball)**

F = m(cannon) a(cannon) F = m(ball) a(ball) Force (exploding gunpowder) is the same for the two equations, they can be combined and re-written m(cannon) a(cannon) = m(ball) a(ball)

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**m(cart1) a(cart1) = m(cart2) a(cart2)**

Acceleration and Mass Force – Spring-loaded plunger m(cart1) a(cart1) = m(cart2) a(cart2)

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**The standard unit of force**

NEWTON The standard unit of force 1 newton = the force required to accelerate a mass of 1 kilogram at 1 meter per second per second

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**1 kg mass x 1 m/s2 acceleration**

1 Newton of Force = 1 kg mass x 1 m/s2 acceleration

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**Newton’s Third Law of Motion**

For every action there is an equal and opposite reaction

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Balloons & Rockets?

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Balloons & Rockets Air inside a balloon is compressed by the balloons rubber walls. The air pushes back so that the inward and outward pressing forces balance. When the nozzle is released, air escapes through it and the balloon is propelled in the opposite direction.

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**Forces become balanced and unbalanced all the time.**

Rocket Flight Forces become balanced and unbalanced all the time.

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**surface of pad pushes the rocket up gravity tries to pull it down**

Apollo 11 Launch pad Balanced surface of pad pushes the rocket up gravity tries to pull it down

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**Thrust from rocket pushes up gravity tries to pull it down**

Engines Ignited Unbalanced Thrust from rocket pushes up gravity tries to pull it down Rocket travels upward Apollo 11

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**Stops at its highest point Gravity pulls it back to Earth**

Rocket in travel – rocket runs out fuel Unbalanced Rocket will slow down Stops at its highest point Gravity pulls it back to Earth Apollo 17 Apollo 11

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Orbiting Satellite

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**Controlling velocity is extremely important for maintaining the circular orbit of the spacecraft**

Only an unbalanced force such as friction with gas molecules in orbit or the firing of a rocket engine in the opposite direction slowing down the spacecraft will bring the satellite out of orbit!

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**Vocabulary Reaction force Pressure Fluid Buoyant force Weight Displace**

Speed Velocity Acceleration Magnitude Vector Inertia Action force Friction Gravity Balanced forces Unbalanced forces Reaction force Pressure Fluid Buoyant force Weight Displace Density Volume Archimedes Principle

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The Nature of Force and Motion 1.Force – A push or a pull – How strong it is and in what direction? 2.Net Force – The sum of all forces acting on an object.

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