1. Physical Science Chapter 12 Matter in Motion

2. 12.1 Measuring Motion An objects change in position over time when compared to a reference point

3. Observing Motion Motion is described as a change in position over time when compared to a reference point. A reference point is a location that appears to stay in place. Reference point

4. Speed The rate at which an object moves it it’s speed. Speed is the total distance traveled divided by the time it took to travel that distance. The SI Unit for speed is m/s Determining average speed Average speed = total distance/ total time

5. Speed Formula D RT Speed (rate)= Distance/Time Distance = Speed x Time Time = Distance/Speed

6. Examples –What is your average speed if you walk 4000m in half an hour? r d t

7. You traveled for 6 ½ hours at 110 km/h. How far did you travel? How long will it take to travel 810 meters at a rate of 15 m/s? d = 715 km d tr d r t

8. Velocity The speed of an object in a particular direction is called velocity Speed – no direction 5m/s Velocity – with a direction 5m/s South Velocity changes if speed or direction changes

9. Combining Velocities Velocities in the same direction can be added: Example 1. Car at 10 m/s 2. Ball at 5 m/s 3. Combined velocity = 15 m/s Velocities in opposite directions work against each other Example 1. Car at 10 m/s 2. Ball at 10 m/s 3. Combined velocity = 0 m/s

10. Acceleration Acceleration is the rate at which velocity changes Acceleration = Final Velocity – Starting Velocity/ Time SI unit for acceleration is m/s/s or m/s 2 Acceleration has a rate and a direction. Acceleration that occurs when velocity increases is positive; acceleration that occurs when velocity decreases is negative or deceleration.

11. Acceleration Examples An airplane goes from 150 m/s to 50 m/s in 20 seconds. What is the acceleration? A car goes from a stop to 21 m/s in 6 seconds. What is the acceleration? A = -5 m/s 2 A = 3.5 m/s 2 Negative acceleration means the object is slowing down. Positive acceleration means the object is speeding up.

12. Spinning is considered to be accelerating continuously since the direction is constantly changing.

13. Graphing Speed DISTANCE TIME Steeper SLOPE means faster speed SLOPE represents speed Shallow SLOPE means slower speed SLOPE = rise = distance run time Y-axis X-axis

14. Graphing Speed DISTANCE TIME SLOPE = rise = distance run time A downward SLOPE (or negative SLOPE) means the object is coming closer. A straight line means the object has stopped moving

15. Graphing Acceleration TIME Slope up-object is moving faster Y-axis X-axis Straight line- object is at a constant speed Slope down- object is slowing down SpeedSpeed

16. 12.2 Force Forces are a push or pull.

17. The SI unit for force is a Newton. Forces are exerted by one object on another object. Net Force is the force that results from combining all forces exerted on an object. All forces must have a magnitude and a direction.

18. Balanced Vs. Unbalanced forces An unbalanced force occurs when the net force is not zero. Unbalanced forces cause a change in motion. They are necessary to cause a non-moving object to start moving. They are also needed to change the motion of a moving object. Balanced forces occur when the net force is zero. Objects with balanced forces will not move.

19. Forces in the same direction are added together to determine net force. example: moving a car 20 N5 N 20 N left + 5 N left 25 N Left

20. Forces in different directions are subtracted from one another. Example: a tug of war (You subtract the smaller force from the larger force) 30 N 20 N 30 N Right - 20 N Left 10 N Right

21. 12.3 Friction

22. Friction is a force that opposes motion between two surfaces that are touching. The amount of friction depends on the force pushing the objects together the roughness of the surfaces Friction occurs because all objects have mass and even smooth objects are not perfectly smooth. “Hills and valleys” are always present.

23. Types of Friction 1. Sliding Friction - one surface grinding over another - example box across the floor 2. Rolling Friction - Friction between wheels and surfaces - example wheels, axles, ball- bearings

24. 3. Fluid Friction - one object moving through a fluid (air, water, oil, etc) - example swimming, flying, parachute, air resistance 4. Static Friction - maximum friction experienced before the object begins to slide, roll or move through a fluid LowHigh

25. Friction can be harmful or helpful. Friction allows us to grip things and to walk. Friction also wears down parts of moving objects. We can reduce friction in many ways. By adding a lubricant, such as grease, wax or oil By changing sliding friction to rolling friction by adding wheels. By sanding a rough surface to make it smoother.