This experiment is one of my favorites in this acceleration series, because it clearly shows you what acceleration looks like. The materials you need is are:

• a hard, smooth ball (a golf ball, racket ball, pool ball, soccer ball, etc.)


• tape or chalk


• a slightly sloping driveway (you can also use a board for a ramp that's propped up on one end)

For advanced students, you will also need: a timer or stopwatch, pencil, paper, measuring tape or yard stick, and this printout.

Grab a friend to help you out with this experiment - it's a lot easier with two people.

Are you ready to get started really discovering what acceleration is all about?

Here's what you do: [am4show have='p8;p9;p12;p39;p92;' guest_error='Guest error message' user_error='User error message' ] 1. Place the board on the books or whatever you use to make the board a slight ramp. You really don’t want it to be slanted very high. Only an inch or less would be fine. If you wish, you can increase the slant later just to play with it.

2. Put a line across the board where you will always start the ball. Some folks call this the “starting line.”

3. Start the timer and let the ball go from the starting line at the same exact time.

4. Now, this is the tricky part. When the timer hits one second, mark where the ball is at that point. Do this several times. It takes a while to get the hang of this. I find it easiest to have another person do the timing while I follow the ball with my finger. When the person says to stop, I stop my finger and mark the board at that point.

5. Do the exact same thing but this time, instead of marking the place where the ball is at one second, mark where it is at the end of two seconds.

6. Do it again but this time mark it at 3 seconds.

7. Continue marking until you run out of board or driveway.



Download Student Worksheet & Exercises Take a look at your marks. See how they get farther and farther apart as the ball continues to accelerate? Your ball was constantly increasing speed and as such, it was constantly accelerating. By the way, would it have mattered what the mass of the ball was that you used? No. Gravity accelerates all things equally. This fact is what Galileo was proving when he did this experiment. The the weight of the ball doesn’t matter but the size of the ball might. If you used a small ball and a large ball you would probably see differences due to friction and rotational inertia. The bigger the ball, the more slowly it begins rolling. The mass of the ball, however, does not matter.

Exercises

1. Was the line a straight line?


2. It should be close now, and the slope represents the acceleration it experienced going down the ramp. Calculate the slope of this line.


3. What do you think would happen if you increased the height of the ramp?


4. Knowing what you do about gravity, what is the highest acceleration it can reach?

For Advanced Students...

[/am4show][am4show have='p9;p39;' guest_error='Guest error message' user_error='User error message' ] Now if you want to whip out your calculators you can find out how fast your ball was accelerating. Take your measuring tape and measure the distance from the starting line to the line you made for the distance the ball traveled in one second.

Let’s say for example that my ball went 6 inches in that first second. Dust off those old formulas and lets play with d=1/2gt² where d is distance, g is acceleration due to gravity and t is time.

We can’t use g here because the object is not in free fall, so instead of g let’s call it “a” for acceleration. Gravity is the force pulling on our ball but due to the slope, the ball is falling at some acceleration less then 32 ft/s².

In this case, d is 6 inches, t is 1 second and a is our unknown.

With a little math we see:

a = 12in/sec² (So our acceleration for our ramp is 12 in/sec² or we could say 1ft/s².)

With a little more math we can see how far our ball should have traveled for each time trial that we did. For one second we see that our ball should have traveled d=1/2 12(12) or d= 6 inches (we knew that one already didn’t we?).

For two seconds we can expect to see that d=1/2 12(22) or d=24 inches. For three seconds we expect d=1/2 12(32) or d= 54 inches.

Do you see why we need a pretty long board for this?

Now roll the ball down the ramp and actually measure the distance it travels after two and three seconds. Do your calculations match your results? Probably not. Our nasty little friend friction has a sneaky way of messing up results. You should definitely see the distance the ball travels get greater with each second however. So make yourself a table or use one of ours to record your data and jot down your calculations and chart your results like a real scientist.

Advanced students: Download your Driveway Races Lab here.

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