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Centuries ago, a scientist named Isaac Newton made many important discoveries. He’s pretty famous so you may have heard of him. He was the first person to figure out the math behind how gravity works, and he laid the groundwork for modern physics. He wrote three simple laws of motion that describe how everything in the universe moves. Now, sometimes physics can seem like it’s hard and maybe even scary but today’s experiment will show you that physics can be fun!
Materials
- Books
- A ruler with a “groove” down the middle
- A few marbles of different sizes
- A small milk carton (like the kind you get with school lunch)
Process
- Stack a few books up and then lean your ruler on them to create a slope. Place the milk carton at the bottom of the slope.
- Place a marble up at the top of the groove in the ruler. Hold it in place with one finger so that when you let it go you’re not pushing it at all. Let it go and watch how far the milk carton moves.
- Repeat that step with marbles of different sizes. How far does each one make the milk carton move? Is it different with different sized marbles? Why do you think this is?
- Now add a few more books to your stack. This makes the ruler slope even steeper. Try your experiment again. Did making the slope steeper change how the marbles moved the milk carton? Why do you think this is happening?
Summary
Isaac Newton’s three laws of motion are pretty simple, and you’re using them all in this marble experiment:
- An object that isn’t moving doesn’t move until something makes it move, and an object that’s moving doesn’t stop until something makes it stop.
- The amount of force a moving object has is equal to its mass (how much stuff there is in it) times its acceleration (how fast it’s speeding up).
- When an object applies a force on another object by pushing or pulling it, the second object applies an equal and opposite force back onto the first object.
When you have a marble sitting on the floor, you have to give it a push to get it going. When you use the ruler as a slope, gravity is all the force you need to make that non-moving marble start moving. That’s the first law right there.
You probably noticed that bigger marbles pushed the milk carton further. This is because of the second law. The bigger marbles have more mass, which means they apply more force onto the milk carton. Basically, they’re heavier, so they push harder. When you stacked more books up you probably noticed that all of the marbles made the milk carton move more than they did with a shorter stack. This is because they’re speeding up more heading down the steep slope, which also makes them push harder.
Finally, when the marbles hit the milk carton, they pushed it forward but then they bounced and moved in a different direction. Some of them might have even stopped! That’s the third law in action. When a marble hits the milk carton, it pushes on the carton, but the carton pushes back and changes how the marble is moving.
The physics of force and motion are pretty simple and easy to experiment with. If you want to expand on this one, try an object that’s heavier than a milk carton. How does that change your results? If you have some toy cars and racetracks, you can try the same experiment with objects that are way heavier than marbles. Try to predict how that will change your results before you try it out.
Want more Saturday Science? See all of our at-home activities on the blog or Pinterest.
