frame of reference

Theres more to motion than objects simply changing position. Youll see why when you consider the following example. Assume that the school bus pictured in the Figure 1.2 passes by you as you stand on the sidewalk. Its obvious to you that the bus is moving, but what about to the children inside the bus? The bus isnt moving relative to them, and if they look at the other children sitting on the bus, they wont appear to be moving either. If the ride is really smooth, the children may only be able to tell that the bus is moving by looking out the window and seeing you and the trees whizzing by. This example shows that how we perceive motion depends on our frame of reference. Frame of reference refers to something that is not moving with respect to an observer that can be used to detect motion. For the children on the bus, if they use other children riding the bus as their frame of reference, they do not appear to be moving. But if they use objects outside the bus as their frame of reference, they can tell they are moving. Q: What is your frame of reference if you are standing on the sidewalk and see the bus go by? How can you tell that the bus is moving? A: Your frame of reference might be the trees and other stationary objects across the street. As the bus goes by, it momentarily blocks your view of these objects, and this helps you detect the bus motion.



defining motion

In science, motion is defined as a change in position. An objects position is its location. Besides the wings of the hummingbird in the opening image, you can see other examples of motion in the Figure 1.1. In each case, the position of something is changing. Q: In each picture in the Figure 1.1, what is moving and how is its position changing? A: The train and all its passengers are speeding straight down a track to the next station. The man and his bike are racing along a curving highway. The geese are flying over their wetland environment. The meteor is shooting through the atmosphere toward Earth, burning up as it goes.

instructional diagrams

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aspects of motion include speed and direction.

-->  a. true

b. false

if you are riding on a bus with a friend, you can tell you are moving by observing the motion of

a) your friend in the seat beside you.

b) the bus driver at the front of the bus.

-->  c) objects like trees and houses outside the windows.

d) two of the above

in question 6, what is your frame of reference for detecting the motion of the bus?

a) your friend

b) the bus driver

-->  c) objects outside the windows

d) two of the above

in question 6, the bus drivers frame of reference is the passenger directly behind him.

a. true

-->  b. false

in question 6, the frame of reference of an outside observer of the bus might be a house across the street.

-->  a. true

b. false

if you are sitting on a stationary bus, which frame of reference might may you think the bus has started moving?

-->  a) the car in the next lane starts moving.

b) a passenger moves to the back of the bus.

c) the bus driver turns to look through the windshield.

d) none of the above

diagram questions

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