JOAN CARTAN-HANSEN, HOST: No where are Newton's laws of force and motion more important than in space exploration.

Let's see how force and motion help us travel the universe.

[MUSIC] Ancient astronomers identified other planets in the solar system.

But it wasn't until Sir Isaac Newton came along that we understood how planets orbit the sun.

BRIAN JACKSON, PROFESSOR OF PHYSICS, BOISE STATE UNIVERSITY: Newton devised the law of gravitation, which told scientists how the force of gravity from the sun acted on the planets to keep them in their orbits.

CARTAN-HANSEN: Newton also developed the three laws of motion.

JACKSON: The first law tells us that a body not being acted on by a force will continue with a constant velocity.

So that means that a body not being acted on by a force will go in a straight line at the same speed forever, or it could be at rest, not moving at all.

Both of those are constant velocities.

If a force acts on that body, then its velocity will change.

That's Newton's second law.

And then Newton's third law tells us that if a body exerts a force on another body, that second body will exert a force back on the first body.

So that's the equal and opposite reaction forces.

All three of these force laws are really important for understanding how bodies move through space.

CARTAN-HANSEN: In fact, we could have never explored space if we didn't understand the laws of force and motion.

Take rockets for example.

JACKSON: If ever you've seen a video of a rocket leaving the launchpad, you'll notice there's all this hot, bright material flying very fast out of the back of the rocket.

Well, that's the rocket pushing on that material.

And Newton's laws tell us that that material pushes back on the rocket and pushes the rocket up off the surface of the earth.

CARTAN-HANSEN: That's Newton's third law: for every action, there is an equal and opposite reaction.

Newton's second law is particularly important for space crafts traveling through space.

JACKSON: Those spacecrafts will proceed through space at more or less a constant velocity because there's no forces acting on them.

So, you don't have to have the rocket constantly firing.

And in fact, most spacecraft spend a long cruise phase without the rocket firing at all, just heading off, and more or less a straight line without the need for any additional propulsion.

CARTAN-HANSEN: That means we can send spacecrafts far away and not need to carry huge amounts of fuel.

Here's where it is important to understand the difference between velocity and acceleration.

JACKSON: So, velocity is how quickly an object is moving through space and in what direction.

So that's velocity.

But acceleration is how quickly is velocity changing.

If you're just cruising along and your speed is a constant and you're not turning to turn it to the right, turn it to the left, then you might have no net accelerations.

That's a constant velocity.

But if you are riding along in a car and you stomp on your brake, you'll slow down.

That's an acceleration.

Your velocity is changing.

You’re slowing down.

Understanding the difference between velocity and acceleration is very important because it's forces that give accelerations.

CARTAN-HANSEN: Newton's laws apply throughout the universe.

Scientists have to apply them when exploring places like mars.

When NASA designed ingenuity, the helicopter that flew on mars, engineers had to build the devise to account for newton's third law.

JACKSON: Mars has a very, very thin atmosphere.

And so, in order for the helicopter to fly, it has to push air down so that the air could push the helicopter up.

Because Mars has a thin atmosphere, there's less air to push.

And so, the Mars helicopter had to have huge propeller blades that spun very, very quickly in order to generate enough, push, enough lift for that teeny tiny helicopter to lift up off the ground.

That same helicopter could have flown very easily in the earth, but it was very difficult for it to fly on Mars because the atmosphere is so much thinner on Mars.

CARTAN-HANSEN: Ingenuity was designed to only fly five times, but it actually made 72 successful flights.

JACKSON: The aerial exploration of the solar system using helicopters like the Mars ingenuity helicopter, that aerial exploration is going to continue with the NASA's dragonfly mission, which will fly on Saturn's icy moon Titan.

Titan is the only moon in the solar system that has a thick atmosphere made mostly of nitrogen.

It's very, very cold, liquid nitrogen temperatures almost, but the atmosphere is also very, very thick compared to the Earth's atmosphere.

The dragonfly mission is itself a helicopter, a rotorcraft.

It will have several propellers that spin very quickly and push on the air.

But because the air is so much thicker on Titan than on the Earth, those propellers don't have to push quite as hard as they would on Mars or even on the earth.

So, dragonfly, even though it's as huge helicopter, it's weighs as much as a small vehicle will actually be easier for it to fly on Titan than it would be for it to fly on either Earth or Mars.

CARTAN-HANSEN: So, space exploration wouldn't be possible, without understanding force and motion.

JACKSON: There's almost no aspect of modern science or modern engineering that doesn't rely at some level on Newton's laws of motion.

The construction of modern buildings, cars, helicopters, almost anything you can think of relies on a very sophisticated understanding of how forces and masses interact.

And that's really all due to Newton.

CARTAN-HANSEN: If you want to learn more about force and motion, check out the Science Trek website.

You'll find it at Science Trek dot org.

[MUSIC] ANNOUNCER: Presentation of Science Trek on Idaho Public Television is made possible through the generous support of the Laura Moore Cunningham Foundation, committed to fulfilling the Moore and Bettis family legacy of building the great state of Idaho.

By the Idaho National Laboratory, mentoring talent and finding solutions for energy and security challenges, by the Friends of Idaho Public Television, and by the Corporation for Public Broadcasting.