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Motion and Forces

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MOTION

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S8P3. Students will investigate relationship between force, mass, and the motion of objects. a. Determine the relationship between velocity and acceleration.

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How are forces and motion related?

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A force is a push or a pull that can result in motion. When a force has been applied to an object and the object moves, work is being done.

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How can motion be described?

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By using a reference point – A (usually) stationary object that helps you detect the motion of an object. (Ex. tree, house etc.)

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Once the reference point is determined you can define motion by speed, position, and direction.

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What is speed?

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Speed refers to how fast an object travels. (Rate at which an object moves.) Depends on: –Distance –Time

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Various forms of speed: –Instantaneous– speed at a given moment (speedometer) –Constant– speed that doesn’t change (cruise control) –Changing– speed that varies (running a mile)

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–Average – speed used when objects are not moving at a constant rate. –Formula: Speed = distance time time

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Ex. If you ran the distance of a football field (91 meters) in 30s, would you run the same speed from start to finish? No, you find the average speed you ran.

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s = d/t s = 91m 30s 30s 3.03 m/s

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How can you graph speed?

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Make up a scenario about what's taking place for each line on the graph

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Two cars traveled at 50 km/h on the same highway. After 2 hours the cars are 200 km away from each other. How is this possible? THEY HAVE DIFFERENT VELOCITIES

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What is velocity? Would you rather know the hurricane’s speed or velocity?

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Velocity – speed of an object in a particular direction. Velocity changes when speed or direction of an object changes. Unit would look like: 5 m/s NW

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Can you have a constant speed but a changing velocity?

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Yes, the Ferris wheel can be moving at a constant speed but its constantly changing direction!

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How is acceleration related to velocity?

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Acceleration – rate of change of speed (velocity) Occurs when an object changes: 1. Speed 2. Direction 3. Both

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What are the types of acceleration?

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Positive Acceleration – speeding up Negative Acceleration – slowing down

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How do you find acceleration? Formula: a= v f –v i a= v f –v i t

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What are velocity/time graphs? Shows change in velocity over time (acceleration).

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Moving at a constant velocity

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Moving at a positive acceleration – velocity changing at constant rate.

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Moving at a negative acceleration – velocity changing at constant rate.

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What is centripetal acceleration?

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Acceleration that occurs in a circular motion; object traveling in a circle is constantly changing directions; so acceleration occurs continuously

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FORCES

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S8P3. Students will investigate relationship between force, mass, and the motion of objects. b. Demonstrate the effect of balanced and unbalanced forces on an object in terms of gravity, inertia, and friction.

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What is a force?

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A force is a push or pull that one body exerts on another. Ex. Friction, gravity, kicking a football. Unit: Newton (N)

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What is a net force?

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The sum of the forces acting on an object.

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What is a balanced force?

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When the forces acting on the object are equal in size and opposite in direction. Net force = 0 (forces cancel each other out) No change in motion occurs!!

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What is an unbalanced force?

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Occurs when forces acting on the object are unequal. Net Force is in the direction of the larger force. (object will move in that direction)

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What is the difference between balanced and unbalanced forces?

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What is Inertia?

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The tendency of an object to resist change.

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Which has a greater inertia?

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Elephant – inertia depends on mass!!

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What is Newton’s 1 st Law of Motion state?

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An object in motion will stay in motion unless an outside force acts upon it. An object at rest will stay at rest unless an outside force acts upon it.

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What is another name for the 1 st Law? The Law of Inertia

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What is the relationship between force, mass, and acceleration?

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Force and Acceleration The greater the force applied to an object the greater the acceleration will be.

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Force and Mass Acceleration will be less on a object that is heavier. –Ex. Softball v. Baseball

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What does Newton’s 2 nd Law state?

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An object will accelerate in the direction of the net force. F = m x a, a = F/m, m = F/a

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What is the unit for force? Newton kg x m/s/s

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Types of Forces

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What is a force that opposes motion between 2 moving objects?

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FRICTION

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What does the amount of friction depend on?

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1.Kind of surface 2. Force pressing surfaces together.

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What is static friction? Friction between two surfaces that are not moving past one another.

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What is sliding friction? Force that opposes motion of 2 objects sliding past one another.

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What is Rolling Friction? Opposing motion between two objects rolling past each other.

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How is friction helpful?

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Without friction the tires could not push against the ground to move the car forward and brakes couldn’t stop the car.

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How can you reduce friction?

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Lubricants – are used to reduce friction. –Ex. Motor oil, wax, grease Switching from sliding to rolling friction Switching from sliding to rolling friction –Ex. Ball bearings between wheel & axles

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S8P5. Students will recognize characteristics of gravity, electricity, and magnetism as major kinds of forces acting in nature. a. Recognize that every object exerts gravitational force on every other object and that the force exerted depends on how much mass the objects have and how far apart they are.

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What is Gravity?

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A downward force Any 2 masses exert an attractive force on each other. Strength of gravitational force depend on: 1.) Mass 2.) Distance

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What is the law of universal gravitation? All objects are attracted to each by gravitational force. –The larger the object – The greater the force –The closer together the object – the greater the force.

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Is weight a force?

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Weight is considered to be a gravitational force that decreases as you move from Earth.

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How can you find weight? F = m x a W = m x 9.8 m/s/s

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What is the difference between mass and weight?

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Mass – how much matter makes up an object –(Doesn’t change as you move from the Earth to the moon.) Weight – considered to be a gravitational force –(Decreases as you move from the Earth to the moon.)

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What is acceleration due to gravity?

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Anything that falls through the air falls at an acceleration of 9.8m/s/s.

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What is Air Resistance?

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Effects anything that is in Earth’s atmosphere. Upward force that opposes gravity of anything falling through the air.

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Air Resistance Depends on 3 things: 1. SPEED 2. SIZE 3. SHAPE of an object.

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If there were no air resistance a hammer and feather would fall at the same time.

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What is a projectile?

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Anything that is thrown or shot through the air.

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Why do projectiles follow a curved path?

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They follow a curved path due to pull of gravity. –Ex: An arrow, Bullet, Basketball

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What is Newton’s 3 rd Law of Motion?

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When one object exerts a force on a second object, the second one exerts a force that is equal and in size and opposite in direction. “Action/Reaction Occurs

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What is Momentum?

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Momentum is related to how much force is needed to change an object’s motion. Momentum = mass x velocity p= m x v

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What is the law of conservation of momentum?

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Momentum can be transferred from one object to another

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What is the relationship between mass and velocity? If two trucks have same velocity, but different masses then... the truck with the larger mass has more momentum

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