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##### Motion & Forces

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**Motion & Forces**Amusement Park 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?**Can you think of examples of forces? • Visible Forces? • Invisible Forces?**Forces can be BALANCED or UNBALANCED**• Balanced forces are equal in size and opposite in direction • Cancel out • Unbalanced forces do not cancel out • Can be in the same direction (add) or opposite direction (subtract) • Result in a NET Force Amusement Park Forces**Unit for Force**• Measured in Newtons (N) • Weight is the measure of the force of gravity • Ex: • Net Force = 30N Net Force = 35N 10N 40N 25N 10N**GRAVITY**A force of attraction between all object. • Depends upon the mass of the objects and the distance between the objects**Galileo Galilei**An English physicist who discovered that gravity pulls all objects toward Earth at the same speed (by shooting cannonballs)**Issac Newton**English Scientist that was able to extend the idea of gravity to all objects in the universe. Universal Law of Gravity All object in the universe exert a gravitational force on each other**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/s2 Gravity in Space**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**Terminal Velocity**When the air resistance equals the force of gravity Terminal velocity is the highest velocity that an object will reach as it falls**What is Motion?**Motion: A change in position of an object compared to a reference point Motion involves all of the following:**What is Motion?**= distance time**What is Motion?**• Acceleration = (Final Velocity –Initial Velocity) • Time**What is Friction?**Friction = A force that opposes or slows down motion • Depends upon the typeof surfaces and the force pressing the surfaces together • Changes motion into heat**What is Friction?**What are some ways athletes uses friction?**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**• 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 e) lawn bowling on a cut and rolled lawn verses an uncut lawn 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**third law: For every action force, there is an equal and oppositereaction 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 • g) sprinklers rotating**Examples of Newton’s 3rd Law**Newton’s third law: "For every action, there is an equal and opposite reaction." When you fire a gun you feel the recoil. Some of the funniest things in cartoons follow physics that have been exaggerated or just plain ignored. Wyle Coyote hangs suspended in space over that canyon for a lot longer than an object would in reality, but it is the anticipation of the drop and Wyle's facial recognition of the upcoming pain that is so classically cartooney. So some laws are stretched for comical effect.**Momentum: The quantity of motion**• A property of moving objects • Calculated by: P = mv • (p = momentum, m = mass, v = velocity) • 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 Rollercoaster Momentum