Inside: This apples and pennies science experiment is a delightful twist on the traditional inclined plane experiments. Can you get an apple up the inclined plane using pennies? How many pennies does it take to get an apple up an inclined plane?

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Kids are born fascinated with inclined planes. Take a baby to the park, and one of the first things she is going to do is start crawling up the slide. “It’s the wrong way,” say parents, but I guarantee you, it’s not the wrong way as far as the baby is concerned. She wants to know how far she can go up before gravity forces her to slide down. This baby is a born scientist.

An inclined plane is just a flat object that is tilted so that one end is higher in space than the other end. People invented them to make their lives easier. An inclined plane helps to reduce the weight of an object. When something is lifted vertically, you support the whole weight of an object. However, when you slide something up the inclined plane, a portion of the weight is supported by the ramp. (Remember this when you study how Egyptian pyramids were built).

Today, instead of pulling an apple up the inclined plane, we are going to have pennies do the job for us.

Since the weather is gorgeous this time of the year, we set up the experiment in our backyard, but you can do it in the living room or classroom. It’s not messy!

How many pennies does it take to get an apple up an inclined plane?

What you need

1. Books (to create an incline)
2. A board (a closet shelf works for us)
3. A yogurt container or a plastic cup for pennies
4. String
5. An apple (maybe even a couple of apples of different size)
6. Lots of pennies
7. A rubber band (it will go around an apple)
8. Hole puncher or scissors to make holes in the containers
9. Paper and pen to record observations

Prep steps

• Poke two holes on two opposite sites of your yogurt container or plastic cup.  

• Thread a string through the holes and tie it security. Your container should look like a little bucket with a handle.  

• Put a rubber band on the apple (so you can connect it to a string). You might have to experiment with a couple of different rubber bands until you find just the right fit.  

• Tie a longish string connecting the plastic container and apple.  

Five-books Incline

We started by making predictions. My 8-year old said that it would take 100 pennies to take our apple up the incline of 5 books. My 5-year old said, “175 pennies!” And I said 50. Who got the closest to the right answer?  Read on to find out.

To set up the experiment:

• Put five books under one end of a board
• set the apple down near the other end of the board
• and hang the plastic container over the higher end of the board.   

The accuracy of this experiment increases dramatically if you eat an apple while performing it!

While counting out loud, start putting pennies into the container.

At what count did the car inch up?  How many pennies did it take to get it all the way up?  

So how many pennies did it take to get an apple up an inclined plane?  In our experiment, it took 63 pennies to get our apple to move a bit and 108 to get it all the way up the ramp.  Your answer would depend on the size and density of your apple and the steepness of your incline.   

It’s hard to believe, but in this fun experiment, kids learn a lot about physics through hands-on investigation. Friction, force, gravity, ramp, the angle of slope, motion, distance are all involved in this simple setup.

Some additional investigation questions

• How changing the angle of an incline by adding a book (or taking one away) will change the number of pennies required?
• What if you replace pennies with quarters?  Will it take fewer or more coins to do the job? (If you tell your kids they can keep all the quarters they use to get the apple up the incline, they will be even more enthusiastic!)
• How can the weight of the apple affect the experiment? (Try this experiment with one small apple and one large apple.)
• My son also immediately wanted to reverse the experiment and find out how many pennies an apple can pull up an incline. (That was fun too!)

Some questions to ask after the experiment

• What are simple machines?
• How do they help people?
• Do you know the definition of the following words: friction, force, gravity, ramp, the angle of slope, motion, distance.

Use our Experiment Sheet to Record the results.

Got an apple and some pennies? You can use them for hours of experimentation and exploration with an inclined plane.

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