This page last changed on Oct 23, 2007 by ehazzard.

## Push it

### Discovery question

Without friction, would an object never stop?

Cannot resolve external resource into attachment.
note: this image should be much smaller.

Explore the effect of friction on objects when you push them.

### Engage

With no friction, would an object never stop?

Imagine a huge lake covered only with ice. Suppose you were on a sled that had no friction at all. If someone gave you a push and you started gliding across the lake, what would happen?
a) You would end up at the other side, going more slowly.
b) You would stop in the middle and not be able to get going again.
c) You would speed up all the way across the lake.
d) You would end up at the other side, going at exactly the same speed as you started.

 L5 currently blank L4 If there were no friction, think about why the sled would slow down or speed up. L3 Think about why the sled would slow down or speed up. L2 What happens if nothing is pushing the sled or slowing it down? L1 You would end up on the the other side going at exactly the same speed because there is no _________.

Explain your answer.
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### Explore

This model shows a box sitting on a level surface. You can give it a shove with the "push it" button. You can also change the friction of the surface it is sliding on.
[insert model]
Try the steel surface. Give the box a push. Watch the motion of the box and the graph.
Describe the motion of the box in words.
TEXTBOX

Look at the graph. How far did the box go before it stopped moving?
NEED TO THINK ABOUT THE RESPONSE - LABEL? TEXT? HINTS ABOUT READING THE GRAPH?

Switch to the "wood" graph. Run the model again. How is the motion of the box different? [NOTE: in the end we need four plots on the same graph can be set up in advance]
TEXTBOX

Look at the graph. How far did the box go before it stopped moving?
NEED TO THINK ABOUT THE RESPONSE - LABEL? TEXT? HINTS ABOUT READING THE GRAPH?

Which material has more friction, steel or woood? Explain how you can tell this from the graphs.
TEXTBOX

Switch to the "carpet" graph. Run the model again. How far did the box go before it stopped moving?
ANSWERBOX

Switch to the "ice" graph. Run the model again. What did the box do this time?
ANSWERBOX

What did the graph do?
ANSWERBOX

### Explain

Which of the four materials has the most friction? Explain how you can tell this from the graph.
TEXTBOX

Which material has the least friction? Explain how you can tell this from the graph.
TEXTBOX

### Elaborate

Using the drawing tool below, draw what you think the graph would look like if the surface had lots of friction.

Draw another line to show the graph if there were no friction at all.
[DRAWING TOOL WITH GRAPH IMAGE AS BACKGROUND-- same graph image as the model's graph ]

### Evaluate

Now the model has a slider to change the amount of friction. Adjust the friction until the model goes exactly 10 m and then stops. Run the model as many times as you like. When you get the right amount of friction, take a snapshot of your graph.

[INSERT model variant, with a friction slider.]

 Document generated by Confluence on Jan 27, 2014 16:49