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Motion & Forces

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. Forces. Forces can be BALANCED or UNBALANCED Not every force causes an object to move!

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Motion & Forces

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  1. Motion & Forces Amusement Park Forces

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

  3. Forces Forces can be BALANCED or UNBALANCED Not every force causes an object to move! • Balanced forces are equal in size and opposite in direction • 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.

  4. Unbalanced forces Can cause an object to start moving, stop moving, or change direction.

  5. Balanced forces have no net force on them, and therefore do not change an object’s motion.

  6. What is Gravity? GRAVITY: An attraction force between all masses in the universe • 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

  7. What is Gravity? • The greater the mass, the greater the force of gravity it exerts • The greater the distance, the less the force • Acceleration due to gravity = 9.8 m/s/s or 9.8 m/s2 This is how fast something accelerates as it is dropped (free-falling) towards Earth Which has more of a gravitational pull on Earth, the sun or the moon? The sun is larger, but the moon is closer! Answer: The moon (remember the moon causes tides!) Gravity in Space

  8. 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, and the object stops accelerating and falls at a constant speed • Terminal velocity is the highest velocity that an object will reach as it falls

  9. 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 the kinds of surfaces and the force pressing the surfaces together • Changes motion into heat (rub your hands together… the friction of your hands rubbing together causes them to get warm)

  10. What is Friction? What are some ways athletes uses friction?

  11. Newton's Laws of Motion

  12. 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

  13. 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

  14. 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

  15. Examples of Newton’s 1st Law

  16. 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

  17. 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)

  18. 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 e) Getting a friend to help you push a heavy box across the room (increased force moves the box faster)

  19. Examples of Newton’s 2nd Law

  20. Examples of Newton’s 2nd Law Definition: 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. Huh?? 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.

  21. Based on Newton’s 2nd law… When driving, why is it more dangerous to pull out in front of a truck loaded with furniture, than it is to pull out in front of an economy car? Answer: the more heavy the vehicle, the harder it is to stop and the more force it will hit you with. Heavy trucks are hard to stop in time to avoid an accident, because it takes more force to slow down a heavy truck than it does a light, economy car.

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

  23. 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

  24. Examples of Newton’s 3rd Law

  25. What do these forces mean? How must thrust relate to drag, in order for an airplane to move forward? How must lift relate to weight, in order for an airplane to lift off the ground?

  26. Work! • You can make an object move if you apply enough force on it. • When you lift a pencil, pull a sled, or push a lawnmower, you are doing work • Work is calculated by the formula: W = f x d (Work = force x distance)

  27. Work? • If a student pushes very, very, very hard against a wall with 200 Newtons of force, and becomes exhausted and covered in sweat, did he do any work? • W= f x d did the wall move? No! Answer: W = 200 N x 0 m • W= 0 Nm (newton-meters) • Was work done? No!

  28. Calculate the work done: • If a student pushes a 50N box (50 newtons, this is the weight of the box) across the room 5.4 meters, how much work was done? • W = f x d • W = 50N x 5.4 m • W = 270 Nm

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