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Published byJette Strøm Modified over 5 years ago
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Anything that changes the motion of an object is considered a force
Forces Anything that changes the motion of an object is considered a force
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Balanced vs. Unbalanced
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Friction and Air Resistance (Forces)
Unbalanced forces that act against motion: Friction Air Resistance Gravity Static Friction – friction between two stationary objects Example: person trying to push a piano Dynamic Friction – friction between one or two objects in motion Example: Car slowing down when driver takes his foot off the gas because of the surface of the road Air Resistance – friction between air and the object in motion Example: A parachute slowing free fall acceleration due to gravity
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Universal Gravitational Force
The gravitational force that one object has on another is directly proportional to its mass and inversely proportional to the distance between the two objects Example 1: The force of gravity is stronger on earth than the moon because the earth has more mass than the moon Example 2: The force of gravity is stronger on the earth’s surface than in orbit because the surface is closer to the center of the earth
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Newton’s 3 Laws of Motion
First Law: Inertia objects in motion will maintain their velocity until a force is applied Example: When a car suddenly stops, the passenger will continue to move unless they are prevented from doing so from a force (wearing a seat belt) Second Law: Fnet = MA The net force that an object has is directly proportional to its mass and acceleration Example: Lighter objects require less force to accelerate than heavier ones (pushing an empty cart vs. a full one) Third Law: Action/Reaction Forces Every action force applied to an object has an equal and opposite reaction force Example The wings of a bird push air downwards. Since forces result from mutual interactions, the air must also be pushing the bird upwards.
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Free Fall and Weight Free fall acceleration is the rate of acceleration of all objects regardless of size due to the force of gravity The acceleration of gravity is 9.81m/s2 for all objects on earth Objects undergoing free fall on another planet of a different size will have a different free fall acceleration value Weight of an object is a force and is equal to its mass times free fall acceleration Weight (Fnet) = mass x 9.81m/s2
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Momentum Momentum is a quantity of motion
It is equal to the mass of an object times its velocity A heavier object will have more momentum than a lighter object travelling at the same speed Momentum of an object changes when a force is applied by another object The total momentum between the two objects is conserved and transferred from one object to another Example: In bowling, the momentum of the bowling ball is transferred to the pins The momentum of the ball decreases when transferred to the pins (motion is slowed) because of the force of the pins on the ball The momentum of the pins increases when the ball strikes because of the force of the ball on the pins
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