Motion and Speed

1. Motion and Speed

2. Answer the following questions on your notes: • Explain in detail how you could tell that the object was moving. • Describe the motion of the object using the things around it. • Define motion without using any form of the term “move” (This means you can not use the words like moved, moving, etc.). • Are there any situations you can think of where detecting motion could be difficult? Explain.

3. Referencepoint Motion • Motion • Change in position in relation to a reference point. Reference Point A non-moving object from which motion is measured

4. Problem: You are a passenger in a car stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward. You have mistakenly set yourself as the reference point.

5. Newton’s First Law • Newton’s First Law of Motion • An object at rest will remain at rest and an object in motionwill continue moving at a constant velocity unless acted upon by a net force.

6. Speed • Rate of motion • Distance traveled by an object divided by the time interval during which the motion occurred (distance traveled per unit of time)

7. Average Speed • Most of the time objects do not travel at a constant speed • You probably do not walk at one constant speed on the way to class • This is why when we talk about how fast an object is moving we are usually talking about its average speed. • If we are talking about an object’s speed at a particular instant in time, you would be describing the instantaneous speed of the object.

8. Let’s practice…. • An athlete swims a distance from one end of a 50 m pool to the other end in a time of 25 seconds. What is the athlete’s average speed? • Average speed = total distance total time Average speed = 50m 25 s Average speed = 2 m/s

9. Problem: • A storm is 10 km away and is moving at a speed of 60 km/h. Should you be worried? • It depends on the storm’s direction!

10. Velocity • Speed in a given direction • Velocity must include speed of an object and direction! • Example: If you were to give the velocity of an airplane and you said it was 600 km/h, you would be incorrect. Why? • You must give a direction. You could say the plane’s velocity is 600 km/h south.

11. Velocity • An object’s velocity changes if either it’s speed or direction changes. • In order for velocity to remain constant, the object must travel on a straight line in the same direction.

12. Acceleration • The rate at whichvelocity changes • Acceleration occurs when an objectchanges speed, direction, orboth • An increase in velocity is calledpositive acceleration. • A decrease in velocity is callednegative accelerationordeceleration.