Catalyst 45.8 km/hr Velocity – is she moving towards you?? 1.Calculate the speed of an object traveling 550km in 12 hours. Use correct units!! 2.Explain the difference between speed and velocity. Use the appropriate vocabulary. 3.The police are tracking an escaped prisoner. Would it be more helpful to know her speed or her velocity? WHY? 4. Velocity of 5 m/s forward to 5 m/s to the right. Is this Acceleration, Deceleration, or Neither 45.8 km/hr Speed is distance divided by time; Velocity is a vector and requires a direction! Velocity – is she moving towards you?? Acceleration – changing direction!

Forces

So, what causes acceleration? Accelerate to the Dark Side, Luke! The Force! No, not that force, but it is FORCE that causes acceleration.

A push or a pull on an object; an interaction FORCE A push or a pull on an object; an interaction

The Measurement of Force 1 Newton is the amount of force required to give a 1 kg mass an acceleration of 1 m/s2 Must have a direction!!! (yup, it is a vector)

Newton http://www.physics.utah.edu/~mohit/offthemark5.gif

Newton http://www.physlink.com/Fun/RickLondon.cfm

What are the units on force? What is Measured Unit(s) Symbol(s) Force N or kg*m/s2 F

FOUR TYPES OF FORCES

An attractive force between two bodies The weakest of all forces GRAVITATIONAL FORCE An attractive force between two bodies The weakest of all forces

ELECTROMAGNETIC FORCE Charged particles at rest exert electric forces on each other Charged particles in motion exert magnetic forces on each other

Holds particles of the nucleus together The strongest of all forces STRONG NUCLEAR FORCE Holds particles of the nucleus together The strongest of all forces

Form of an electromagnetic force WEAK FORCE Form of an electromagnetic force Happens when some nuclei radioactively decay

(Gravity Force) = (mass) x (gravity) Mass is measured in grams or kilograms (kg). Gravity is ALWAYS = 9.8m/s2

Calculate your gravitational force! F=m*g (1lb = 0.454 kg) (100lb = 100 x 0.454 kg) = 45.4kg F = (45.4kg)(9.8m/s2) = 444.92N

What is the force weight of a 45 kg desk? 441 N What is the force weight of a 12 kg dog? 117.6 N How much does a 35 N cat weigh? 3.57 kg (÷9.8)

NEWTON’S FIRST LAW

Newton’s First Law An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction, unless acted upon by unbalanced forces

Possibilities of Newton’s 1st

Newton’s First Law Also known as “The Law of Inertia”

WEARING YOUR SEATBELT IS THE LAW… …THE LAW OF INERTIA!

Objects at rest tend to stay at rest, objects in motion tend to stay in motion, unless acted on by an unbalanced force

the tendency of an object to resist changes in motion INERTIA the tendency of an object to resist changes in motion

Generally speaking, the more mass an object has, the more inertia it has.

the tendency of an object to resist changes in velocity INERTIA the tendency of an object to resist changes in velocity

the tendency of an object to resist changes in acceleration INERTIA the tendency of an object to resist changes in acceleration

Supertankers illustrate the principal of inertia; their engines are cut off a mile or more before the tanker enters port and it still coasts right on in.

For Example… No motion! It stays at rest!

The toy will stay in motion until….what? When a hand pulls one ball, it’s that unbalanced force we mentioned… Voila! Motion! The toy will stay in motion until….what? It is acted on by an unbalanced force.

BALANCED AND UNBALANCED FORCES

BALANCED FORCES (no acceleration)

UNBALANCED FORCES (motion / velocity / acceleration)

Forces are either balanced, or unbalanced When forces are equal, no acceleration occurs.

Forces are either balanced, or unbalanced But when they are unbalanced, that’s when objects accelerate

Forces are either balanced, or unbalanced But when they are unbalanced, that’s when objects accelerate

Forces are either balanced, or unbalanced But when they are unbalanced, that’s when objects accelerate

Forces are either balanced, or unbalanced But when they are unbalanced, that’s when objects accelerate

NET FORCE all forces acting on an object the sum of again…it’s a VECTOR!

When an object is in equilibrium (acceleration = 0), Net Force= 0 (also called a Balanced FORCE!)

Practice Finding the Net Force __________ -2 N Left Hint: Make sure to have a number and a direction…

Practice Finding the Net Force __________ 50 N Left

Practice Finding the Net Force __________ 0 N No direction

Practice Finding the Net Force __________ 15 N Up

The object accelerates in the direction of the net force, the vector sum. What happens when more than one force acts on something at the same time?

NEWTON’S SECOND LAW

Newton’s Second Law The net force acting on an object causes an object to accelerate in the direction of that force

Law #2: The acceleration of an object depends on the object’s mass and the strength of the outside force acting on it.

Acceleration under Newton’s 2nd An object will only accelerate if an unbalanced net force is acting on it! The direction of acceleration is the direction of the net force

Relationships of Newton’s 2nd If you double the net force, you double the acceleration (if mass is held constant) If you double the mass, you halve the acceleration (if force is constant)

Newton’s Second Law Applied (here gravity = 10m/s2)

Air Resistance Why does the elephant fall faster than the feather? The force of gravity on the earth is ALWAYS 9.8 m/s2. Air Resistance is the MAIN factor! Air resistance is a type of FRICTION! The elephant has a greater mass and therefore has less air resistance. The feather, due to it smaller mass is more vulnerable to air resistance! This is WHY the elephant falls faster!!

Law #2: The acceleration of an object depends on the object’s mass and the strength of the outside force acting on it. If the forces acting on them are equal, who is going to accelerate more? Fat Albert or Rudy?

Calculating With Newton’s Second Law. F = 300 N m = 1500 kg a = ? Plug and Chug What is the acceleration of a 1,500 kg cow when it is pushed by a force of 300 N?

Whiteboard Practice What is the acceleration of a 300 kg walrus being pulled by a force of 1,000 N?

What if we know acceleration? One step further... What if we know acceleration? A 30,000 kg rocket accelerates at 10 m/s2. How much force is acting on it?

Force Practice Problem If Rebeka pushes a 100kg box so that it accelerates 4m/s2, how much force does she apply to the box?

Whiteboard Practice A 90 kg person is pushed with a force of 100 N. What is her acceleration? A cannon ball is shot out of a cannon with an acceleration of 10 m/s2. If its mass is 100 kg, how much force does the cannon fire with? What is the mass of a cart if a horse pulls it with a force of 500 N and accelerates it by 0.5 m/s2?

Forces don’t cause motion, forces cause ACCELERATIONS! Accelerations cause MOTION!

FRICTION

FRICTION the force that opposes the motion between two surfaces in contact

Types of Friction Static Friction—friction between 2 things not moving past each other Sliding Friction (Kinetic)—friction between 2 things that are moving Rolling Friction (Kinetic)—friction between a rolling object and the object it rolls on

Comparing Friction For an equally massed object of the same substance: Rolling Friction is less than Sliding Friction which is less than Static Friction

Friction applied to a stationary object Static Friction Friction applied to a stationary object

Friction applied to a moving object Kinetic Friction Friction applied to a moving object

Kinetic friction is always LESS than static friction. WHY: Molecular forces form on stationary objects.

Friction depends on the two surfaces involved.

TERMINAL VELOCITY

TERMINAL VELOCITY The point at which a falling object ceases to accelerate and falls at a constant rate. Gravity reaches an equilibrium!

NEWTON’S THIRD LAW

For every action, there is an equal and opposite reaction Newton’s Third Law For every action, there is an equal and opposite reaction

For every “action force” there is an equal in size and opposite in direction “reaction force”

Newton’s 3rd Law …is a great one. Very poetic. It goes like this: For every action, there is an equal and opposite reaction.

Let’s see an example. ACTION: Rocket Gases push DOWN on air. REACTION: Air pushes up on rocket.

Try this one: REACTION: Air pushes UP on wings. ACTION: Wings push DOWN on air. REACTION: Air pushes UP on wings.

…And another! ACTION: Feet push back on the floor. REACTION: Floor pushes forward on feet.

Identify 6 pairs of action-reaction forces in the following picture

Action = reaction means the bowler and the ball get equal and opposite forces when the ball is launched. But since the bowler’s mass is greater than the ball’s mass, the bowler accelerates less than the ball. ma = ma

To get cart B to go the greatest distance, who should go on which cart? Rudy Fat Albert

How do Newton’s Laws explain what happens next? Newton’s First Law: Science English An object at rest will stay at rest. Neither cart will move until it’s pushed or pulled.

How do Newton’s Laws explain what happens next? Newton’s Second Law: Science English An object’s acceleration depends on its mass and the force acting on it. Fat Albert will not accelerate as much as Rudy.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How do Newton’s Laws explain what happens next? Newton’s Third Law: Science English For every action force there is an equal reaction force acting in the opposite direction. Rudy and Fat Albert will be pushed with the same force, in opposite directions.

How would the following be examples of Newton’s 3rd Law? A fish swimming through the water A bird flying through the air A car moving forward