Do now A baseball player holds a bat loosely and bunts a ball. Express your understanding of momentum conservation by filling in the tables below. http://www.physicsclassroom.com/Class/momentum/u4l2b.cfm

a: +40 (add the momentum of the bat and the ball) c: +40 (the total momentum is the same after as it is before the collision) b: 30 (the bat must have 30 units of momentum in order for the total to be +40)

Motion What causes objects to move?

Forces A push or pull on an object Measured in Newtons (N) Causes movement Stops movement Determine the amount of movement Measured in Newtons (N) Instrument – Spring Scale http://www.ftschool.org/fourth/science/images/springScale.jpg

Are these forces balanced?

What affect do balanced/unbalanced forces have on motion? Balanced: No change in velocity Therefore constant speed or no motion. Unbalanced: Always cause a change in motion. Acceleration

Newton’s 1st Law of Motion an object in motion will stay in motion at the same velocity unless a net force acts on it! an object at rest will remain at rest unless a net force acts on it! (- the law of Inertia)

Example What is newtons’ first law of motion? How does this demonstrate it?

a.k.a. Law of Inertia Inertia: the property of an object (matter) that resists any change in velocity - to make an object move (or stop) you must overcome it’s inertia

Formula Inertia Equation (the easiest one this year!) Inertia = mass (unit = kg) (Inertia = m)

What are the outside forces that act on the object?

Friction A force that opposes motion Causes objects to slow down Direction of the force is opposite the motion The pushing force needs to be greater than the frictional force acting on the object for it to begin to move. http://home.clara.net/darvill/enforcemot/friction.htm

3 Types of Friction Static Friction- tries to prevent an object from moving Sliding Friction- slows down an object sliding on a surface Rolling Friction- needed to make a wheel turn -wheels reduce the amount of friction by reducing the surface area touching between surfaces

Can Friction be beneficial? YES! Walking Writing

How can friction be reduced? Oil Ball bearings Ice

Do Now What are the forces that slow down or speed up motion? Friction Gravity Air resistance

Gravity A force of attraction between any two objects with mass Controlled by mass and distance

Gravitational Force Attraction between objects Depends on: Mass Greater the mass = Greater the gravitational force Distance Smaller the distance = Greater the gravitational force Less Gravitational Pull Greater Gravitational Pull Greater Gravitational Pull Less Gravitational Pull

Less pull of gravity = Greater Jump Earth is 6x larger than the moon Moon Gravity = 1/6 of the Earth Gravity Not drawn to scale

What is the difference between mass and weight? Mass: how much matter an object is made of. Weight- measure of the force of the (Earth’s) gravity on an object Example Earth  weight = 180 lbs. Moon  weight = 180lbs. = 30 lbs

Acceleration due to Gravity On Earth = 9.8 m/s² Everywhere on Earth the force of gravity is the same so acceleration of a falling object is a constant number. Although, this would only be constant in a vacuum. (an area with no atmosphere)

What can slow down a falling object? Air! Air Resistance: the force of air opposite the motion of an object in an atmosphere -force is controlled by the shape of the object (aerodynamics) -force increases as the objects speed increases

Will the object always accelerate? No, eventually the force of air resistance equals the force of gravity.

Terminal Velocity -forces become balanced -speed becomes constant Terminal Velocity- maximum velocity reached by a falling object in an atmosphere -forces become balanced -speed becomes constant -the object is still falling!

Why does the elephant hit the ground first?

Do Now What is the value (number) of the acceleration due to gravity? What force causes objects to slow down as they fall? Define Terminal Velocity

Newton’s 2nd Law the acceleration on an object increases as the net force acting on the object increases acceleration is in the direction of the force

f = m*a The force exerted on the object is equal to the objects mass times the acceleration. You can also solve for mass or acceleration. The unit for force is the NEWTON (N)

Practice Problems A 20 kg object was accelerated at a rate of 6 m/s². What force was applied to it? . F = ma F = (20)(6) F = 120 N

A force on an object accelerated it a rate of 7. 5 m/s² A force on an object accelerated it a rate of 7.5 m/s². The object had a mass of 50 kg. What was the measure of the force? F = ma F = (50)(7.5) F = 375 N

A force of 150 N was applied to a 10 kg object A force of 150 N was applied to a 10 kg object. What was the acceleration produced? . a = F a = 150 a = 15 m/s² m 10

An object was accelerated at rate of 35 m/s² from a force of 700 N An object was accelerated at rate of 35 m/s² from a force of 700 N. What would the mass of the object have been? . m = F m = 700 m = 20 kg a 35

Exit Ticket Calculate the force required to push the block to the right. Calculate the force if you doubled the mass of the box. What is the relationship between force and mass? 100kg 25m/s²

Do Now Define Newton’s first 2 Laws of Motion Describe what forces are acting on a falling object from the time it starts falling to the time it reaches its terminal velocity

Newton’s 3rd Law to every action there is an equal and opposite reaction (for forces) Action-Reaction Pairs of Forces Action- one object exerts a force on a second object Reaction- the second object exerts an equal but opposite force on the first

Consider a fish in the water

For years, space travel was believed to be impossible because there was nothing which rockets could push off of in space in order to provide the propulsion necessary to accelerate. This inability of a rocket to provide propulsion is because ... a. ... space is void of air so the rockets have nothing to push off of. b. ... gravity is absent in space. c. ... space is void of air and so there is no air resistance in space. d. ... nonsense! Rockets do accelerate in space and have been able to do so for a long time.

In the top picture (below), Kent Budgett is pulling upon a rope which is attached to a wall. In the bottom picture, the Kent is pulling upon a rope which is attached to an elephant. In each case, the force scale reads 500 Newtons. Kent is pulling ... a. with more force when the rope is attached to the wall. b. with more force when the rope is attached to the elephant. c. the same force in each case.

Exit Pass Describe how Newtons 3rd Law of motion works to propel the shuttle into space. If the shuttle has a downward force of 5000N, what is the upward force of the ground on the shuttle? Explain your answer.