1. MATTER IN MOTION Chapter 5

2. Measuring Motion Even if you don’t see anything moving, motion is still occurring all around you. What are some examples of motion occurring around us?

3. Reference Point You might think that the motion of an object is easy to detect – you just watch the object. But you are actually watching the object in relation to another object that appears to stay in place. The object that appears to stay in place is a reference point. When an object changes position over time relative to a reference point, the object is in motion.

4. Speed Speed is the distance traveled by an object divided by the time taken to travel that distance. To calculate average speed take total distance and divide it by total time. ave speed = total distance / total time Why calculate average speed and not speed only?

5. Velocity Velocity is the speed of an object in a particular direction. Do not confuse the terms speed and velocity. If you reference an object’s velocity you must indicate in direction in which it is traveling. An object’s velocity is constant only if its speed and direction don’t change.

6. Combining Velocities Imagine that you are riding in a bus that is traveling east at 15 m/s. If you walk toward the front of the bus at 1 m/s east, you now have a combined or resultant velocity of 16 m/s east. If you walk toward the back of the bus at 1 m/s west you now have a combined or resultant velocity of 14 m/s east.

7. Acceleration Acceleration is the rate at which velocity changes. Remember that velocity changes only if speed changes, direction changes, or both change. An increase in velocity is commonly called positive acceleration. A decrease in velocity is commonly called negative acceleration or deceleration.

8. Average Acceleration Find average acceleration by using the following equation: average acceleration = final velocity – starting velocity / time it takes to change velocity See page 122 in your textbook.

9. Circular Motion An object travelng in a circular motion is always changing, so it is accelerating. The acceleration that occurs in circular motion is known as centripetal acceleration. Centripetal acceleration occurs on a Ferris wheel at an amusement park or on a merry go round.

10. Force A force is simply a push or a pull. All forces have both size and direction. A force can change the speed, velocity, or acceleration of an object. Anytime you see a change in an object’s motion you can be sure that the change in motion was created by a force. Force is measure in a unit called the newton (N).

11. Forces Acting on Objects All forces (a push or or a pull) act on objects. All objects push or pull back on forces that are pushing or pulling on them.

12. Net Force A net force is the combination of all of the forces acting on an object. If forces are going in the same direction, you add them together.  +  If forces are going in the opposite direction, you subtract one from the other.  -  If the net for is 0, there is no movement.

13. Balanced Forces When the forces on an object produce a net force of 0 N, the forces are balanced. Balanced forces will not cause a change in the motion of a moving object and a balanced force will not cause a nonmoving object to start moving.

14. Unbalanced Forces When the net force on an object is not 0 N, the forces on the object are unbalanced. Unbalanced forced produce a change in motion, such as change in speed or a change in direction. Unbalanced forces are necessary to cause a nonmoving object to start moving.

15. Friction Friction is a force that opposes motion between two surfaces that are in contact (touching each other). Objects are not completely smooth, they are covered with hills and valleys. These hills and valleys cause resistance between the touching surfaces. Roughness and surface area affects the amount of friction between objects.

16. Types of Friction Kinetic friction is moving (rolling and sliding) friction. This is friction between moving surfaces Static friction is non-moving friction. This is when a force is applied to an object but the force does not cause the object to move. Static friction disappears as soon as an object starts moving, and then kinetic friction immediately occurs.

17. Harmful and Helpful Friction Make a list of how friction can be harmful. Make a list of how friction can be helpful. How can friction be reduced? How can friction be increased?

18. Gravity Gravity is a force of attraction between objects that is due to their masses. The force of gravity can change the motion of an object by changing its speed, direction, or both.

19. Effects of Gravity on Matter All matter has mass. Gravity is a result of mass. Therefore, all matter has gravity. There is a gravitational attraction between all objects. Since the Earth’s mass is huge, its gravitational attraction on objects is also huge.

20. Sir Isaac Newton For thousands of years, people asked two very puzzling questions. Why do objects fall toward Earth, and what keeps the planets moving in the sky? These two questions were treated separately until 1665 when a British scientist named Sir Isaac Newton realized that they were two parts of the same question.

21. Newton Made a Connection Newton made a connection between objects which fall to the earth and the moon which moves around the earth. He proposed that these two forces are actually the same force – a force of attraction we now call gravity. Newton summarized his ideas about gravity in a law now known as the law of universal gravitation - universal because it applies to all objects in the universe.

22. The Law of Universal Gravitation Part 1: Gravitation Force Increases as Mass Increases. Part 2: Gravitational Force Decreases as Distance Increases.

23. Mass vs Weight Mass is the amount of matter in an object. Mass of an object does not change. Weight is a measure of the gravitational force on an object. Weight of an object can change.