♪Intro♪.

One of the best parts of our day here at the Fort is checking our email. We get so many awesome science questions!

Even though we can’t answer them all, today Squeaks and I wanted to answer some of them! Okay, our first question is from Kelsey. Kelsey wants to know, “Why is it harder to run uphill and easier to run downhill?” Interesting question, Kelsey!

It’s easier to run down a hill than up a hill because of gravity, which is a force that pulls you — and everything else on the planet — toward the ground. Forces are the pushes and pulls that happen to us and all around us every day. When you push a block along the floor or roll a ball, you’re putting a force on it!

Gravity is a force, too, and it’s pulling on us all the time, even though we can’t see it. But we sure can feel what gravity does! Like, when I jump into the air … like that ...

I don’t stay up for very long because gravity pulls me right back down to the ground. The reason I was able to be in the air for even a little bit is because of another force: the push I made against the floor with my legs. I pushed down with my legs hard enough to overcome gravity, but only for a second.

Now, if I push down harder …. I can jump higher …. But it takes more work.

The same kind of thing happens when we run up a hill. Our legs are trying to push our bodies up, while gravity is pulling us /down/. We have to work hard to fight the pull of gravity, and more work means we get tired faster!

The opposite happens when we run down the hill. This time, we get a little help from gravity, since gravity is pulling us down — the same direction that we want to go. We’re not fighting against the gravity, so it doesn’t feel like we’re working as hard.

Thanks for your question, Kelsey! Our second question today is from Matty. Matty asked us, “How can insects climb walls and be upside down?” That’s an awesome question!

If I tried to climb a wall, gravity would pull me right back down! So how do flies and other insects do it? Gravity pulls on everything — even the tiniest fly!

Well, some insects have special body parts that help them to climb up walls and across ceilings. Because a wall or ceiling that looks or even feels pretty smooth to us, really isn’t. If we could look at a wall really closely, we’d see that they have lots of little bumps, cracks, and pits.

And what seems like a tiny bump to us can look like a comfortable place to stand for a tiny fly! Some insects have little claws or hairs on the ends of their legs, which they use to help them grab onto the bumps in the wall or ceiling. There are also some insects that make an oily liquid that helps them to stick to a wall or ceiling.

It’s sticky enough to keep their bodies from falling down, but not sticky enough that they get stuck in one place! Thanks for your awesome question, Matty! We love getting comments and mail!

So if /you/ have a question for us, ask a grownup to help you leave a comment below, or to send us an email at kids@scishow.com! We’ll see you next time, here at the Fort! ♪Outro♪.