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Warm Up 510.25.11 What causes motion? In other words, what causes things to start, stop and change directions? Sorry, computer issues have made me use a powerpoint from the web

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Dynamics - the study of what causes motion

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Aristotle (384-322 BCE) Greek philosopher who arrived at several principles of nature. Greeks did not use experimentation because they believe that the senses can be deceived- the correct way to do science is to think about it. He proposed the 2 Types of Motion a. Natural Motion b. Violent Motion

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Natural Motion Occurs when objects fall to rest on the surface of the earth or when they are sailed up into the sky, like a puff or smoke. Objects seeking their natural place in the world.

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Violent Motion Occurs when a moving object is moved away from its natural place, such as picking up a bottle from the ground or throwing the ball into the air. The object in violent motion must be kept in motion by a violent force or it will come to rest

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Aristotle vs Galileo Aristotles views were widely held for centuries. It wasnt until Galileo came along that his theories were completely disproved.

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6 Notions of Force and Motion 1.) If there is motion there is force acting. 2.) There cannot be a force without motion- if there is no motion then there is no force acting. 3. When an object moving there is a force in the direction of motion.

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6 Notions of Force and Motion 4.) A moving object has a force within it which keeps it moving. 5.) A moving object stops when its force is used up. 6.) Motion is proportional to force acting. Therefore a constant speed result from a constant force.

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Answers? NOT one of these notions are correct. These are 6 commonly held misconceptions of force and motion, and they all originate form Aristotles views.

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Galileo (1564- 1642) Conceived of motion as continuous. Conceived of motion on a frictionless surface An object once placed in motion, will move further until another force brings it to stop. Implied that the natural state of objects is continuous motion.

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Galileos Breakthrough He realized that things slowed down due to friction. He called it RESISTANCE He called it RESISTANCE In order to understand force and motion, you need to envision motion without friction.

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INERTIA Objects on frictionless surface has it. Objects will never stop, will go forever. Objects needs no force to keep it moving Newton incorporated this into his work and called the property inertia.

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Newstons First Law The Law of Inertia When no external, unbalanced force acts on an object its velocity remains constant. or If no net force acts on an object, it maintains its state of rest or its constant speed in a straight line or An object at rest will remain at rest, an object in motion will remain in motion in a straight line unless either are acted upon by an external force.

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Implications External force is required to change the velocity of an object. External force must be unbalanced. Helps explain the behavior of objects in motion- they resist change in motion due to their inertia.

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Mass a measure of inertia Inertia is directly proportional to the mass of the object. Inertia is directly proportional to the mass of the object. A large object at rest is hard to move. A large object having constant velocity is hard to stop. Mass is defined as the amount of matter in an object. In the book it is defined as the laziness of an object.

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Example An elephant at rest has a lot of laziness so it has a greater tendency to remain at rest. (hard to move)

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Example A runaway train at constant velocity has a lot of laziness so it has a greater tendency to stay in motion. (hard to stop)

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Differentiating Mass and Weight A given quantity of mass will remain the same wherever it is in this physical world. The weight depends on the mass of an object and it is equal to the force of gravity on an object.

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Examples If you have a mass of 75 kilograms, your mass on earth, moon and Jupiter will be 75 kilograms. Your weight depends on the force of gravity exerted on you by the other mass (earth, moon and Jupiter).

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MASS and WEIGHT are DIRECTLY PROPORTIONAL TO EACH OTHER. MASS and WEIGHT are DIRECTLY PROPORTIONAL TO EACH OTHER. More mass means more weight. Conversion of your weight in pounds to your mass in kilograms. 2.2 pounds = 1 kilogram

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MASS and WEIGHT are DIRECTLY PROPORTIONAL TO EACH OTHER. If your weight is 50 lbs, what is your mass in kg? 50 lbs ( 1 kg/ 2.2 lbs) = 22.73 kg The earth is pulling you with a force of 50 lbs towards its center. Also equal to a force of 490 newtons. Do you want your weight to be in newtons? to be in newtons? 50 lbs = 490 newtons 50 lbs = 490 newtons

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NET Force resultant force. Which object will remain at rest, according to Newtons First Law? Which object will continue moving with constant velocity, according to Newtons First Law? 5 N 8 N This car will accelerate. The cat will move

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Light Bulb Moment No matter how many applied forces are acting on an object AND the net force is equal to zero, the object will maintain its inertia. Balanced forces on an object, maintains the state of inertia of an object.

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If the forces acting on an object are cancelled, the object is said to be in a state of equilibrium. Meaning the net force is equal to zero and the object maintains its inertia. Weight Air Friction The object is at rest Normal Force by the ground Falling objects will experience terminal velocity

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Example If you are standing, at rest, the balanced forces acting on you are: If you are standing, at rest, the balanced forces acting on you are: a.) your weight and b.) the upward support force of the ground called the normal force. normal force.

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Questions 1. Why do professional photographers use heavy cameras for their shots? 2. While making a turn to the right, why is your body moving towards the left side of the car? 3. Why do we use safety seat belts? 4. In which location will it be difficult to shake a 50 kg rock, on earth or in space?

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Questions 5. Which object has more inertia, a 15 kilogram bowling ball or a 15 kilogram bag of pure cotton? 6. While standing still what is your inertia with respect to the sun? with respect to the ground? respect to the sun? with respect to the ground? 7. What is the value of the normal force if you are standing on the table? 8. If you throw a ball horizontally and we neglect air friction and the force of gravity, how will you describe the motion of the ball?