# Motion & Forces.

## Presentation on theme: "Motion & Forces."— Presentation transcript:

Motion & Forces

What is Motion? Motion: A change in position of an object compared to a reference point Motion involves all of the following:

The rate of change in position
What is Motion? Speed The rate of change in position Speed = distance ÷ time or = distance time

Velocity What is Motion? Speed plus direction
Example: 50 km/hour north

Acceleration What is Motion? The rate of change in velocity
Positive acceleration = speeding up Negative acceleration = slowing down (decelerate) Acceleration = Vfinal – Vinitial Time or = ∆Velocity

Motion Questions ) What units are used to measure speed?
) What units are used to measure acceleration? ) What is another way to say “slowing down” in terms of acceleration?

Answer this in the “In” for Forces

What is a Force? FORCE = Any push or pull which causes something to move or change its speed or direction

What is a Force? Forces can be BALANCED or UNBALANCED Balanced forces are equal in size and opposite in direction Arrow thickness is equal. Net Force = 0. Balanced forces result in no movement.

What is a Force? Unbalanced forces in the same direction Net Force =
Forces can be BALANCED or UNBALANCED Unbalanced forces in the same direction Arrow thickness is not equal. Net Force = When two forces act in the same direction, the net force is the sum of the two individual forces. Box moves right

What is a Force? Forces can be BALANCED or UNBALANCED Unbalanced forces are not equal in size and/or opposite in direction. If the forces on an object are UNBALANCED, we say a NET force results. Net force = Box moves right.

“Out” Force Questions ) What famous physicist are units of force named after? 2) If Moby has a mass of 50 kg and Tim has a mass of 40 kg, who would require more force to move?

Gravity and Friction New Cornell notes (in, out, through) for gravity and friction.

In For Gravity and Friction
Does a person have gravity?

What is Gravity? GRAVITY: An attraction force between all masses
Newton’s universal law of gravitation: Every object in the universe exerts a gravitational attraction to all other objects in the universe The amount of gravitational force depends upon the mass of the objects and the distance between the objects

What is Gravity? The greater the mass, the greater the force
The greater the distance, the less the force Acceleration due to gravity = 9.8 m/s/s or 9.8 m/s2

What is Weight? Weight is a measure of the gravitational force between two objects The greater the mass the greater the force (weight) Measured in units called Newtons (N) In the standard system units are pounds (lbs)

“Out” Gravity Questions
) How does the gravity on the moon compare to the gravity on Earth? ) Why don’t you notice your own gravitational pull on the Earth? ) On what two things does the force of gravity depend?

What is Friction? Friction = A force that opposes or slows down motion
Caused by the physical contact between moving surfaces The amount of friction depends upon 2 things: 1.) kinds of surfaces and 2.) force pressing the surfaces together Changes motion into heat

What is Friction? 4 Types of Friction:
Rolling Friction (bike tire on the road) Sliding Friction (book sliding on table) Fluid Friction (object moving through air or water) Static Friction (force holding things still)

Air resistance: The force of air exerted on a falling object
The air pushes up as gravity pulls down Dependent upon the shape and surface area of the object When the air resistance equals the force of gravity, terminal velocity is reached Terminal velocity is the highest velocity that an object will reach as it falls

The feather reaches terminal velocity quickly
The feather reaches terminal velocity quickly. Air resistance and gravity cancel each other out so the feather stops accelerating. The elephant keeps accelerating due to its shape, surface area and mass.

An Elephant and a Feather both fall at the same rate when air is removed (vacuum).
Apollo astronauts dropped a feather and a hammer during their lunar experiments. Both landed at the same time.

Examples of Friction? What are some ways athletes use friction?

Friction and Gravity “Out” Activity.

Newton's Laws of Motion

Newton's Laws of Motion First Law: An object at rest stays at rest or an object in motion, stays in motion (in the same direction/at the same speed) unless acted upon by an unbalanced force Also called the law of inertia

Inertia is: A property of matter
The tendency of an object to resist any change in its motion The greater the mass the greater the inertia The greater the speed the greater the inertia

Examples of Newton’s 1st Law
a) car suddenly stops and you strain against the seat belt b) when riding a horse, the horse suddenly stops and you fly over its head c) the magician pulls the tablecloth out from under a table full of dishes d) the difficulty of pushing a dead car f) car turns left and you appear to slide to the right

Newton's Laws of Motion Second law: The greater the force applied to an object, the more the object will accelerate. It takes more force to accelerate an object with a lot of mass than to accelerate something with very little mass. The player in black had more acceleration thus he hit with a greater amount of force

Newton's Laws of Motion Second law:
The greater the force, the greater the acceleration The greater the mass, the greater the force needed for the same acceleration Calculated by: F = ma (F = force, m = mass, a = acceleration)

Examples of Newton’s 2nd Law
a) hitting a baseball, the harder the hit, the faster the ball goes b) accelerating or decelerating a car c) The positioning of football players - massive players on the line with lighter (faster to accelerate) players in the backfield d) a loaded versus an unloaded truck

Examples of Newton’s 2nd Law
The second law states that unbalanced forces cause objects to accelerate with an acceleration which is directly proportional to the net force and inversely proportional to the mass. This one is telling us that big heavy objects don’t move as fast or as easily as smaller lighter objects. It takes more to slow down a charging bull then to slow down a charging mouse.

Newton's Laws of Motion “In” Activity
How can climbing into a boat from a dock be used to explain Newton’s 3rd Law?

Newton's Laws of Motion third law: For every action force, there is an equal and opposite reaction force. (Forces are always paired)

Examples of Newton’s 3rd Law
rockets leaving earth guns being fired c) two cars hit head on d) astronauts in space e) pool or billiards f) jumping out of a boat onto the dock

Examples of Newton’s 3rd Law

Examples of Newton’s 3rd Law

Momentum: The quantity of motion
A property of moving objects Calculated by: P = mv (p = momentum, m = mass, v = velocity) Calculating Momentum Momentum Practice

Momentum: The quantity of motion
Law of conservation of momentum: the total amount of momentum of a group of objects does not change unless outside forces act on the objects This is an Inelastic collision. Notice how there is no bounce. The Diesel engine’s momentum before the collision is _________ The Diesel engine + the flat car momentum after the collision is _________. No momentum was lost or gained.

Newton’s Laws Out Activity
) Why does a ball roll across a rug and come to a stop? ) What is a net force? ) Give an example of Newton’s 3rd Law: