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Force and Motion 7th Gr. Science

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Motion A change in position of an object compared to its reference point. More simply, motion is moving from point A to point B A change in position of an object compared to its reference point. More simply, motion is moving from point A to point B

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Reference Point When observing motion, the object that stays in place is called the reference point. Identify reference points from the pictures below. When observing motion, the object that stays in place is called the reference point. Identify reference points from the pictures below.

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Speed / Velocity Speed is the rate at which an object moves in a given amount of time. Speed is a measure of the Rate of motion. Total Distance Traveled = Average Speed Total Time Traveled Velocity: speed in a particular direction Speed is the rate at which an object moves in a given amount of time. Speed is a measure of the Rate of motion. Total Distance Traveled = Average Speed Total Time Traveled Velocity: speed in a particular direction

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Speed Maurice ran a 100 m dash in 9.73 seconds. What was his average speed? 100m / 9.73 sec = ? Maurice ran a 100 m dash in 9.73 seconds. What was his average speed? 100m / 9.73 sec = ?

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Acceleration Acceleration is a change in speed or direction of an object. Acceleration = A A = change in velocity time Velocity = V = Distance Time V f - V i t Acceleration is a change in speed or direction of an object. Acceleration = A A = change in velocity time Velocity = V = Distance Time V f - V i t

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Types of Motion Free Fall Circular Motion Projectile Motion

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Free Fall Motion An object in free fall will accelerate in a straight line at a rate of 9.8m/s/s This is the rate in the absence of air resistance.

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Free Fall After falling for 1 second the little man will be going 9.8 m/s After falling for 2 seconds the little man will be going 19.6 m/s How fast will the elephant be going after 1 sec.? After 3 sec.?

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Free Fall - Air Resistance Air Resistance will slow down the acceleration of gravity. That’s why parachutes work. That’s why a feather falls slower than a ball.

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Free Fall - Air Resistance After accelerating to about 200 km/h or 55.6 m/s. This sky diver will go no faster because air resistance will balance acceleration. How many seconds will it take for him to reach maximum speed?

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Circular Motion - Centripetal Force Moving objects want to move in a straight line. To move in a circle, the object must be held to the center by a force. This is centripetal force.

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Circular Motion - Centrifugal Force Circular Motion creates a force moving out in the opposite direction as centripetal force. This is centrifugal force

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Circular Motion If the centripetal force is removed the object will begin to move in a line. Hammer Throw and Discus work this way.

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Circular Motion Which force keeps cars on the track even when they are upside down? Which force is provided by the white steel track?

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Projectile Motion An object that moves horizontally but also is affected by the downward pull of gravity is in projectile motion.

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Force Any push or any pull Only unbalanced forces are able to accelerate or change the motion of objects. Any push or any pull Only unbalanced forces are able to accelerate or change the motion of objects.

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Force gives an object energy to move, stop moving, or change direction. Blowing your nose, riding your bike, or just breathing all require force A flag is blown by the force of the wind. A jet is pushed forward by the force of its engines. A flag is blown by the force of the wind. A jet is pushed forward by the force of its engines.

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Friction Friction is a force that opposes motion. Friction acts in a direction opposite to the direction of motion of the object.

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Balanced Forces Forces occur in pairs and can be either balanced or unbalanced. Balanced forces DO NOT cause a change in motion. They are equal in size and opposite in direction.

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Balanced Force-No Motion If the force in each direction is equal, they cancel each other out and the resulting force is zero. Therefore, there is no change in motion.

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Unbalanced Forces Unbalanced forces are not equal and opposite. Unbalanced forces will cause motion.

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Unbalanced Forces If opposing forces are NOT equal, then the force will be in the direction of the greater force. Who wins the arm wrestling contest?

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Unbalanced Forces Who wins the tug of war contest?

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Unbalanced forces Forces can be applied in the same direction

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Force Problems Two important things to remember when working with combined forces Forces in the same direction combine by addition Forces in Opposite directions combine by subtraction

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Newtons A Newton (N) is a unit to measure force. The force of 1 Newton can accelerate a 1Kg object to increase its speed 1 meter per second for each second. One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s2 A Newton (N) is a unit to measure force. The force of 1 Newton can accelerate a 1Kg object to increase its speed 1 meter per second for each second. One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s2

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Force and Direction Force is a quantity that has both magnitude (Newtons) and direction. This determines if an object will move, and in which direction. The book in the picture is sliding to the right. It will stop when the force to the right is less than 5N. Force is a quantity that has both magnitude (Newtons) and direction. This determines if an object will move, and in which direction. The book in the picture is sliding to the right. It will stop when the force to the right is less than 5N.

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Force Problems Two tugboats are moving a barge. Tugboat A exerts a force of 3000 newtons on the barge. Tugboat B exerts a force of 5000 newtons in the same direction. What is the combined force on the barge?

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Force Problems Draw arrows showing the individual and combined forces of the tugboats in #1.

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Force Problems Now suppose that Tugboat A exerts a force of 2000 newtons on the barge and Tugboat B exerts a force of 4000 newtons in the opposite direction. What is the combined force on the barge?

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Force Problems Draw arrows showing the individual and combined forces of the tugboats in #3.

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Force Problems Could there ever be a case when Tugboat A and Tugboat B are both exerting a force on the barge but the barge doesn't move? Draw arrows showing the individual and combined forces in such a situation.

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Sir Isaac Newton Isaac Newton 1643-1727 Newton was a great mathematician and scientist. He took observable natural phenomena and found mathematical relationships

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Newton’s Principia This book is widely recognized as the greatest scientific book ever written. He provides science with a unified way of looking at the natural world. He lays out the mathematical relationship to the observable physical world.

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Big Idea Gravity The attractive force of two masses like the earth and an object on its surface. Gravity makes a falling object accelerate at 9.8m s 2

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Another Big Idea White light can be divided into colors with a prism. The colors always have a specific sequence. ROY G. BIV

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Another Big Idea The Planets are held in their revolutions by gravity. They are not sucked into the sun because of balanced forces Centrifugal Force = Gravity We won’t fly into space and we won’t crash into the sun.

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Newton’s Laws of Motion Newton described three laws of motion Inertia Force = mass X acc. Reaction

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1st Law (Inertia) And object at rest will stay at rest. Unless it is acted on by an unbalanced force

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1st Law (continued) An object in motion will continue moving in a straight line at a constant speed. Unless it is acted on by an unbalanced force.

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2nd Law If you apply force to an object it will accelerate or change its velocity in the same direction as the force. Force = Mass X Acceleration F = ma If you apply force to an object it will accelerate or change its velocity in the same direction as the force. Force = Mass X Acceleration F = ma

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2nd Law If you push twice as hard, the object will accelerate twice as much. If the object has twice as much mass, it accelerates half as much. A speeding bullet and a slow train can each kill you for different reasons. Explain.

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3rd Law For every reaction, there is an equal and opposite reaction Force back - move forward Force down - move up If you push something, it pushes back

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