Motion and Speed

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.

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

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.

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

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)

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.

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

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!

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.

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.

Acceleration The rate at which velocity changes Acceleration occurs when an object changes speed, direction, or both An increase in velocity is called positive acceleration. A decrease in velocity is called negative acceleration or deceleration.