Speed is how far something goes in a set time. Measure both, and you have it.
Speed How far something travels in a certain time.
Step 1: Something to Notice
Watch first. The explanation comes later.
Two runs look nearly identical. One pushes the block 10 cm and the other pushes it 18 cm.
How much can you trust what you saw?
Step 2: Find Out
Run each speed and write down the energy and the distance each time.
Step 1 — Predict
Speed 3 and speed 4 look very similar. How different are their energies?
Choose what you think will happen. You cannot see the experiment until you do — guessing first is what makes it worth watching.
Step 3: So Here Is Why
Now the explanation, after you have seen it happen.
Put it in a table
One row per run. Then you can compare runs instead of remembering them.
Then look for the pattern
With the rows next to each other, the rule shows up: divide one by another and check.
Keep everything else the same
Change the speed and only the speed, or you will not know what caused the difference.
A number beats a word
"Fast" means different things to different people. Distance divided by time gives a number anybody can check and compare. Turning an impression into a measurement is what makes it evidence.
measure To find out how big, long, or heavy something is, using numbers.
A graph shows the pattern
Plotting distance against time makes a steady speed a straight line and a changing speed a curve. The shape says something the individual numbers do not.
Step 4: A Common Mistake
Lots of people think
“You can tell which is faster just by watching.”
Step 5: Why Scientists Write Everything Down
The same idea somewhere new.
A result you remember is a result you can be talked out of. A result in a table can be checked by somebody who was not there, which is the whole reason science can be argued about at all.
Step 6: Think It Through
Practice makes it stick.
Two Similar Runs
Problem 1 of 1
Speed 3 gives 9 units and speed 4 gives 16. What is the difference?
units
Measuring Properly
1 of 4
What is speed?
2 of 4
Why put results in a table?
3 of 4
How far does the block go at speed 6, mass 1?
cm
4 of 4
To find out what the speed does, what must stay the same?
Step 7: Quick Check
Show what you know.
Question 1 of 1
Two runs looked nearly the same. Their energies were 9 and 16. What does that tell you?
Step 8: Explain It in Writing
Claim, evidence, then reasoning.
The question
Somebody says a heavier cart always hits harder than a lighter one. Using your readings from this chapter, write an argument saying whether they are right.
Evidence you can use
- Mass 1 at speed 4 gave an energy of 16.
- Mass 3 at speed 2 gave an energy of 12.
- Mass 3 at speed 4 gave an energy of 48.
- Mass 1 at speed 2 gave an energy of 4.
- Doubling the speed from 2 to 4 took the energy from 4 to 16.
- Doubling the mass from 1 to 2 took the energy from 4 to 8.
Words to usemassspeedenergyfour timesdoubledsquared
Fill in all three boxes. The reasoning box is the one that matters most.
What You Found Out
- Speed is how far something goes in a certain time.
- Record every run in a table so runs can be compared.
- Change one thing at a time.
- Small differences in speed make large differences in energy.