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MOTION AND FORCES

MOTION AND FORCES. CHAPTER 1 NOTES. REFERENCE POINT. An object that appears to stay in place.

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MOTION AND FORCES

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  1. MOTION AND FORCES CHAPTER 1 NOTES

  2. REFERENCE POINT • An object that appears to stay in place If your car is moving in the same direction and same speed as the bus, the bus will appear to not move with respect to you. Of course, if you compare the speed with the ground, both of you will be moving at some velocity.

  3. COMMON REFERENCE POINTS • Earth’s surface • Trees, buildings, ground • Plane, bus, cars, skateboard

  4. MOTION • When an object changes position over time relative to a reference point.

  5. SPEED • The distance traveled by an object divided by the time taken to travel that distance. • Formula for speed (average speed): distance/ time or total distance/total time

  6. VELOCITY • The speed of an object in a particular direction • Example: The airplane’s speed is 650 mi/hr. The airplane’s velocity is 650 mi/hr west.

  7. CONSTANT VELOCITY • Speed and direction never changes. • Motion along a straight line. • Velocity changes if speed or direction (or both) changes. ? – A Ferris wheel spins at a constant speed but not at a constant velocity. Explain.

  8. RESULTANT VELOCITY • The combination of 2 or more velocities. • When 2 velocities are in the same direction, you add them. • When 2 velocities are in the opposite direction, you subtract them. The resultant velocity is in the direction of the larger velocity.

  9. ACCELERATION • The rate at which velocity changes. • Velocity changes if speed changes, if direction changes or if both change. • POSITIVE ACCELERATION – increase in velocity • NEGATIVE ACCELERATION – decrease in velocity

  10. FORMULA FOR ACCELERATION • Final velocity – starting (initial) velocity time

  11. CENTRIPETAL ACCELERATION • Acceleration that occurs in a circular motion

  12. FORCE • A push or a pull • Has both size and direction • Can change the acceleration of an object

  13. NEWTON • Unit for force • (N)

  14. NET FORCE • Combination of all forces acting on an object.

  15. BALANCED FORCES • When forces on an object produce a net force of 0 N.

  16. UNBALANCED FORCES • When the net forces on an object is not 0 N.

  17. FRICTION • A force that opposed motion between two surfaces that are in contact. • Causes a moving object such as a ball to slow down and stop.

  18. 2 FACTORS THAT AFFECT AMOUNT OF FRICTION • Amount of force: the more the surfaces push together (more mass), the more the surfaces come into close contact with each other, so the more friction. Objects that weigh less, has less friction. 100 g  10 grams 2. Roughness of the surface: rough surfaces have more microscopic hills and valleys than smooth surfaces. So the rougher the surfaces, the greater the friction.

  19. 2 Types of Friction • Static Friction: when a force is applied but the object does not move • Static friction is overcome when a force acting on it is large enough, then kinetic friction takes place

  20. TYPES OF FRICTION • KINETIC FRICTION: friction between moving surfaces 3 types: sliding, rolling, fluid

  21. FRICTION : HARMFUL • Car parts, and engine – wear and tear from heat of friction • Wear out your sneakers and shoes • Wear out tires • Erosion of top soil

  22. FRICTION : HELPFUL • Allows you to write with a pencil • Allows you to walk without slipping • Treads of shoes allow you to walk

  23. WAYS TO INCREASE FRICTION • Make surfaces rougher • Increase force pushing on surfaces Phone book friction 1 Friction Bill Nye

  24. WAYS TO REDUCE FRICTION • Use lubricants (substances that are applied to surfaces to reduce the friction between surfaces) such as oil and wax • Sliding to rolling friction • Make surfaces smoother

  25. GRAVITY: A FORCE OF ATTRACTION • GRAVITY: a force of attraction between objects that is due to their masses • Can affect position of object or the direction of the object’s motion • All objects are attracted to other objects, but you do not feel it because the force is so small that the object does not move. • Earth’s gravitational force is strong enough to feel, so that’s why objects fall to the ground. Gravity Bill Nye Gravity Bill Nye 2

  26. LAW OF UNIVERSAL GRAVITATION • Describes the relationship between gravitational force, mass and distance.

  27. MASS vs WEIGHT • Weight is the measure of gravitational force, use a spring scale to measure, unit is Newton or pounds • Mass is the amount of matter in an object, use a triple beam balance to measure, unit is grams, kilograms • Weight and mass are the same on Earth, but go to the moon or another planet and the weight changes. The mass DOES NOT CHANGE. Weight depends of the force of gravity. The amount of matter will stay the same.

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