2013
May 01

Newton’s Laws of Cake (Law #3)

by Hannah Holt »

12 comments


Oh boy! It’s time for the last law.

Newton’s Third Law of Motion states that for every action there will be an equal and opposite reaction. In other words:

Newton’s Third Law of Motion Cake: If you push cake, it pushes back.

Now that may seem like a weird idea. How can cake push? It doesn’t even have arms.

Well, let’s look at Newton Bunny. Here he is skating on Galileo’s Pond:

Newton skating

What would happen if we placed a giant chocolate cake right in front of him?

Newton skating cake

SMACK! The cake hits him.

Now wait a minute! Does he hit the cake or does the cake hit him? The answer is both. It takes two sides to create a reaction. If Newton didn’t hit the cake, he wouldn’t put a dent in the cake. And if the cake didn’t hit him back, he would just somehow pass through it like it was a ghost-cake.

So Newton hits the cake and the cake hits him back. Like this:

bunny pushing cake

Newton is pushing a cake and the cake pushes just as hard back. So the cake stays where it is and so does Newton.

But cake is just cake, and eventually it reaches a point where it can’t push back any harder. What if Newton pushes cake beyond its pushing limit?

bunny pushing cake unbalanced force

Anytime there is an unbalanced force something changes to balance it. The extra force is converted into motion. In Newton’s case, he falls into the cake.

bunny falls into cake2

Uh, oh! Newton pushed too hard. He fell into the cake.

So if you push something, it pushes back, otherwise you would fall through it.

Here’s a little review. See if you can fill out these activity sheets:

skating bunny worksheet

wall pushing worksheet

(Answers: Top – any path is fine, but once the bunny hits the cake he will be forced to stop. Bottom – The bunnies on the left hand side of the page will push the wall over because the bunny is pushing harder than the wall pushes back.)

SNEAKY FORCES:

In my last post I mentioned we would be discussing sneaky forces. These are forces you can’t see. Newton’s Third Law says that every action requires a reaction. So if something changes (reacts), you need an action. According to Newton’s First Law of Motion, if you threw a cake into the air, it would keep sailing up, up, and away. But cake won’t do that. Eventually it comes crashing down to the ground. Splat! Even though you can’t see it, something is pulling the cake down. Do you know what it is? Which of the following sneaky forces do you think is acting on the cake in the air?

sneaky forces

Gravity is the reason a cake falls to the ground. Here are some other stories. See if you can identify the sneaky force at work.

1) A cake is sliding along a table. No one touches it, but it comes to a stop anyway. What stopped the cake?
2) Buster Bunny delivered a cake to his cousin in jail. He baked a saw into the cake. A police officer with a magnet took the cake away from him without touching the cake. What force took the cake?
3) A cake resting on ice is placed next to a fan. The fan is turned on, and the cake slides away from the fan. What moved the cake?

Here are the answers:

1) Friction, 2) Magnetism, 3) Wind

So there you have it. Now you know all about Newton’s Three Laws of Motion Cake. Here are the three laws in review:

Newton’s 1st Law of Cake: Cake on a plate will not get up and start moving by itself. If the cake is moving, it will keep going until something stops it.

 

Newton’s 2nd Law of Cake: If you want to punch a cake harder, you must either hit it with something bigger or punch it faster.

 

Newton’s Third Law of Cake: If you push cake, it pushes back.

And now for a really nerdy aside: I’m a civil engineer and my husband is a physicist. We were having a discussion/disagreement about Newton’s Third Law. Now my husband is the kindest man I’ve ever met, but he didn’t like the way I was treating Newton’s Third Law, so he said, “Well, you just don’t think about motion because you’re a civil engineer. Civil engineers never do any work.” I had to laugh because he’s right. The whole point of civil engineering is avoiding work… Work is Force multiplied by Distance (W = F×d), and civil engineers build stationary objects. We make things that bend an wiggle but hopefully nothing that moves too much. Movement is the domain of mechanical engineers. So civil engineers build airports and bridges, and mechanical engineers build airplanes and cars. Also here is a free body diagram of cake being eaten by an alligator.

alligator2

Don’t worry, my husband and I resolved our disagreement and the above is physicist approved.

Have fun with physics! And go smash some cake!


  1. julie rowan zoch

    I’m sold already – really I would buy this PB!!! And though you don’t ‘know’ me, I can assure you I DO NOT BUY MANY BOOKS! Just sign me up, will ya!

  2. Joanna

    julie said it!! and I am so in love with your bunny!

  3. Beth MacKinney

    When is this going to be available?

  4. Carrie F

    I really think you have to do this, Hannah. It’s too much to resist. I see a trilogy…

  5. Renee LaTulippe (@ReneeMLaTulippe)

    Hannah, I’ve said it before and I’ll say it again: you are brilliant. These need to be PBs ASAP. Only you can do it. You are one of a kind.

  6. grandpa weight

    Looks like every one wants you to publish this–not just aunt ginger. LOL

  7. Erin Forbes

    Hi Hannah,
    I’m a first year teacher in Australia and former book editor. This is fantastic! Publish it as a picture book and teachers will buy it! Promise!

    • Hannah Holt

      Thanks, Erin. Best wishes with your first year of teaching!

  8. Alexa

    THANK YOU so much for these amazing resources. I wish you could see my K-2 graders excitement every friday when I teach science. It is all because of you and Newton bunny. They loved every minute of your activities and lessons. They are so obsessed with Newton, that they want to make their own Newton bunny. Do you have a coloring page of Newton Bunny that we could use and attach to craft sticks?

    • Hannah Holt

      Thank you, Alexa! This kind of feedback makes me so happy. I’m send you an email with requested material. If you don’t receive it in the next 24-hours, let me know and I’ll post the coloring page for you here.

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