This post is written by guest blogger, Mary Kate Warner .

Science Experiment: Pumpkin Sink-or-Float

Children are always amazed over what will sink and what will float. In this case, they’ll see that a pumpkin will float (shhh!) unless it has been punctured. Once there’s a hole in a pumpkin, and the unwanted water to saturate it; it will sink. It’s a lot like our faith. Whether we sink or swim as Christians depends on how well we’ve protected ourselves against wrong influences. 


  • One pumpkin, small enough that you can submerge in a bucket of water.
  • Bucket of water, filled three-quarters of the way up.
  • Sharp knife

Sink or Float Experiment (with teacher’s words):

Let’s play Sink or Swim. How many of you think the pumpkin will sink in this bucket of water?

Let them take a vote on sinking or swimming. Declare its approximate weight and ask whether or not that will play in. Ask them why they think it will sink or swim. Let’s find out.

But before I submerge the pumpkin, let me remind you that we can “sink or swim” in our Christian walks. Jesus declares that he will rescue all drowning people if they cry out to him, but who wants to get in a position like that?

What does choosing good friends have to do with whether we sink or swim with Jesus?

Let them give answers, which should include that the wrong friends can distract you from God or influence you to do things God wouldn’t want.

Just so we’re clear on that, let’s find out about this pumpkin. Drop it in the water; it will float. Congratulate those who guessed correctly. Here’s what’s involved in sinking and floating. It has less to do with the weight of the object and more to do with what’s inside it. An object that weighs more than water will sink—unless that object is full of air. Air weighs less than water, and if trapped inside something, like this pumpkin, it will counteract the weight of the pumpkin. That’s why the pumpkin floats—it is hallow. But let’s look what happens when we put a couple of holes in it.

Keeping the knife away from hands and fingers, puncture the pumpkin twice, one near the bottom and once near the top. Move the knife around so that you have a clear opening and not just a “slit” that can ooze shut again.  Put the pumpkin back in the water. It will slowly start to sink.

What’s happening is that the air that was trapped in the pumpkin now has a way to escape. The pumpkin is filling with water, and that’s forcing the air out of the top. Two scientific principles apply here:

• First: Water displaces air; because water is heavier than air, it will force air out as if fills something;

• Second: Objects will sink when they are filled with their own likeness. As the water replaces the air, it adds its own weight to the pumpkin, and therefore, it sinks. Let’s pretend the pumpkin is like us. The air is like God’s indwelling, which we also call the Holy Spirit. The water is “the world” or the bad things of the world that we don’t want to get inside of us, like sinful ideas, selfish behavior, violence, or meanness.

Hold up the knife.

Let’s say this knife is like a bad influence. It’s like that friend who does sinful, selfish, or mean things.

Hold up the pumpkin over the bucket so it drips into it.

What happens when we let people like that get too close to us? When we start hanging out with them, we let them sleep over, we sit next to them every day at lunch…They can “puncture” us. The rules of science are a lot like the rules of the spirit.

First: Sinful people are flesh and blood, and we can hear them and see them and touch them and listen to them. So even though it’s not true, sometimes they can seem more real than God. If they start “filling us up” with bad ideas, the Holy Spirit can “rise up” and decide He’s more comfortable outside us than inside us.

Second: If we get filled up with what’s outside of us—the bad ways of the world—we can start to sink in our faith. Next time we pick a friend, rather than asking how much fun he is or what kind of a bike he has that we might ride…let’s ask: Will this person help me sink or swim with my faith? Water displaces air; because water is heavier than air, it will force air out as if fills something; Sinful people can begin to fill us up, and the Holy Spirit works for us less and less. Next time you pick a friend ask yourself: Will this person help me sink, or will he/she help me swim with Jesus?

If you enjoyed this Pumpkin “Sink Or Float” activity by Mary Kate Warner, please leave a comment below and let me know!

The above post was written by guest blogger, Mary Kate Warner. For questions about this activity, please reach out to her personally at Christianity Cove.