1st Law3rd Law

2nd Law

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

We only We only identifyidentify the the principles that exist in the principles that exist in the physical world and name physical world and name

them for reference!!them for reference!!

What makes objects move?What makes objects move?

What makes them change their motion?What makes them change their motion?

ForceForce

Contact ForceContact Force – when 2 objects – when 2 objects must be touching to exert forces on must be touching to exert forces on each othereach otherFriction Pushing or kicking a ball

Long-Range ForceLong-Range Force – a force that is – a force that is exerted without the objects having to exerted without the objects having to touchtouchGravity Magnetism Nuclear force

Force – a push or a pullForce – a push or a pull

Net forceNet force – combination of all forces acting – combination of all forces acting on an objecton an object

COMBINING FORCESCOMBINING FORCESCOMBINING FORCESCOMBINING FORCES

Balanced ForcesBalanced Forces – 2 or more forces acting – 2 or more forces acting on an object cancel each other – they do NOT on an object cancel each other – they do NOT change the motion of the object (Net Force = 0)change the motion of the object (Net Force = 0)

Unbalanced ForcesUnbalanced Forces –forces acting on an –forces acting on an object do NOT cancel each other – they DO object do NOT cancel each other – they DO change the motion of the object (Net Force change the motion of the object (Net Force ≠ 0)≠ 0)

RESTREST

The state of an object when it is not The state of an object when it is not changing position.changing position.

THIS IS RELATIVE!!THIS IS RELATIVE!!

Not moving in relation to your immediate Not moving in relation to your immediate surroundings!!!surroundings!!!

MOTIONMOTION

The state of an object when it is changing The state of an object when it is changing position in relation to its surroundings.position in relation to its surroundings.

THIS IS RELATIVE, TOO!!THIS IS RELATIVE, TOO!!

When you are sitting on an airplane, When you are sitting on an airplane, you are at rest, but if you get up and you are at rest, but if you get up and

walk down the aisle, you are in motion.walk down the aisle, you are in motion.

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

rest!

If rest were defined as If rest were defined as a total absence of a total absence of

motion, it would not motion, it would not exist in nature.exist in nature.

UNBALANCED FORCESUNBALANCED FORCES

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

If an object is in If an object is in MOTIONMOTION, it takes an , it takes an unbalanced force to unbalanced force to stop itstop it, , change change its directionits direction from a straight line path, from a straight line path,

or or alter its speedalter its speed. .

ACCELERATIONACCELERATION

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.

Newton’s 1Newton’s 1stst Law of Motion Law of MotionNewton’s 1Newton’s 1stst Law of Motion Law of Motion

Lazy, resistant to change!!!Lazy, resistant to change!!!

Newton’s 1Newton’s 1stst Law of Motion Law of Motion If there is If there is NONO net force acting on an object then 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.

Newton’s 1Newton’s 1stst Law of Motion 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!!!

Newton’s 1st Law of MotionNewton’s 1st Law of Motion

MASS OF AN OBJECT = INERTIA OF AN OBJECT

More mass = more inertia

More mass = more inertia

(greater resistance to change

(greater resistance to change)

Less mass = less inertia

Less mass = less inertia(smaller resistance to change)

(smaller resistance to change)

Newton’s 1st Law of MotionNewton’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.

Newton’s 2Newton’s 2ndnd Law of Motion Law of MotionForce is equal to mass times acceleration

Newton’s 2Newton’s 2ndnd Law of Motion Law of Motion

Cannon

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 - REACTION @ work

What happens to the cannon and the ball is determined by Newton’s 2nd Law.

Newton’s 2nd Law of MotionNewton’s 2nd Law of Motion

F = m(cannon) a(cannon)

F = m(ball) a(ball)

Force (exploding gunpowder) is the same Force (exploding gunpowder) is the same for the two equations, they can be for the two equations, they can be

combined and re-writtencombined and re-written

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

Acceleration and MassAcceleration and Mass

Force – Spring-loaded plunger

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

NEWTONNEWTON

The standard unit of force

1 newton = the force required to accelerate a mass of 1 kilogram

at 1 meter per second per second

1 Newton of Force =

1 Newton of Force =

1 kg mass x 1 m/s

1 kg mass x 1 m/s22

acceleration

acceleration

Newton’s Third Law of MotionNewton’s Third Law of Motion

For every action there is an equal and For every action there is an equal and opposite reactionopposite reaction

Balloons & Balloons & Rockets?Rockets?

Balloons & RocketsBalloons & Rockets

Air inside a balloon is Air inside a balloon is compressed by the balloons compressed by the balloons rubber walls.rubber walls.

The air pushes back so that The air pushes back so that the inward and outward the inward and outward pressing forces balance.pressing forces balance.

When the nozzle is released, air When the nozzle is released, air escapes through it and the balloon is escapes through it and the balloon is propelled in the opposite direction.propelled in the opposite direction.

Rocket FlightRocket Flight

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

Launch padLaunch pad

BalancedBalanced

surface of pad pushes the rocket surface of pad pushes the rocket upup

gravity tries to pull it gravity tries to pull it downdown

Apollo 11

Engines IgnitedEngines Ignited

UnbalancedUnbalanced

Thrust from rocket pushes Thrust from rocket pushes upup

gravity tries to pull it gravity tries to pull it downdown

Rocket travels upwardRocket travels upward

Apollo 11

Rocket in travel – rocket runs out fuelRocket in travel – rocket runs out fuel

UnbalancedUnbalanced

Rocket will slow downRocket will slow down

Stops at its highest pointStops at its highest point

Gravity pulls it back to EarthGravity pulls it back to Earth

Apollo 17

Apollo 11

Orbiting SatelliteOrbiting Satellite

Controlling velocity is extremely important for maintaining the circular

orbit of the spacecraft

Only an unbalanced force such as Only an unbalanced force such as frictionfriction with gas molecules in orbit or with gas molecules in orbit or

the the firing of a rocket enginefiring of a rocket engine in the in the opposite direction slowing down the opposite direction slowing down the spacecraft will bring the satellite out spacecraft will bring the satellite out

of orbit!of orbit!

VocabularyVocabulary ForceForce SpeedSpeed VelocityVelocity AccelerationAcceleration MagnitudeMagnitude VectorVector InertiaInertia Action forceAction force FrictionFriction GravityGravity Balanced forcesBalanced forces Unbalanced forcesUnbalanced forces

Reaction forceReaction force PressurePressure FluidFluid Buoyant forceBuoyant force WeightWeight DisplaceDisplace DensityDensity VolumeVolume Archimedes PrincipleArchimedes Principle