GO IN DEPTH

# Gravity Launch

#### Materials

• A Gravity Launch activity sheet for each student
• A beanbag (or other non-breakable objects that can be dropped to the floor for demonstration)
• Pencils or pens
• Computers with Internet access

There are a lot of challenges with space flight. One is simply getting the rocket off the ground. This is because the thrust to launch a rocket has to work against the force of gravity. So, there are two forces at play in this game: earth’s gravitational pull and thrust. Your kids will play with a computer interactive that demonstrates these two forces in action.

### Background

All objects exert gravitational force on all other objects. But the strength of gravitational force an object exerts has to do with mass. In order for something, like a rocket ship, to get off the ground, a force (stronger than earth’s gravitational pull) needs to be exerted on it. Once a rocket ship is out in space, it can be pulled by other objects and will orbit an object if it begins to fall toward that object. When something orbits earth, or the moon, it is actually freefalling.

### Activity Instructions

Set-Up

Hold a bean bag and let it drop to the floor. Ask kids: “Why do you think the bean bag went down instead of up or sideways?” (It’s such a common occurrence, kids may think of it as a “natural” one without some explanation.)

Now, make an X on the floor with masking tape and stand back from it. Ask: “How could I get the bag to hit the X? Do I need to toss at a certain angle or use a certain forceful toss? Does a stronger toss keep the bag in the air longer? Why?” (Answers may vary. Encourage the kids to explain their answers.)

Gather around a computer and pull up the Gravity Launch interactive and press start. Explain that you are trying to get the rocket ship to orbit earth. Plug 6 into the thrust and hit return, leave the angle at 15 and hit the launch button.

The rocket ship will crash into the earth. Ask kids: “What pulled the rocket ship back to earth? What will it take to get the ship to orbit earth?” (This may be a good opportunity to go over the concepts of thrust and angle. Thrust is the force the engines of rocket boosters produce to push it (the rocket) off the ground. The force needs to be strong enough to overcome earth’s gravity. The angle we’re talking about here is the launch angle, which is the initial elevation angle of the rocket once it is launched.)

Now plug 6.5 into the thrust and the rocket ship will go orbit the moon. Ask: “Why is it orbiting the moon?” (This is an opportunity to point out that things in space, like the moon, also have a gravitational force.)

Plug in 6.5 for the thrust again and discuss why the angle of the rocket ship is important.

Now kids can do Gravity Launch alone or in small groups.

Activity

Give each child a Gravity Launch activity sheet and a pencil and point them toward the student web page. The activity sheet will provide kids with the URL to access the interactive. If this activity is too difficult for your group, you may want to do the whole interactive together.

Here are some correct thrust and angle settings for each mission, 1-5, of the interactive:

 Mission Thrust Angle Thrust Angle 1 6.35 50.844 OR 6.7 17.699 2 6.9 31.5 OR 7.0 34.624 3 7.112 42.506 OR 8.0 37 4 7.0 45.9 OR 7.6 12.39 5 6.9 52.251

Give kids about ten minutes to do the first launch. This is a generous amount of time, but unless they are being systematic about the settings, it could take this long. You also may want to ask some follow up questions to help gauge understanding. Here are some questions you could ask:

1. Did anyone have their rocket ship pulled back to earth for a crash? (This will likely happen to some of your students since any thrust setting below six does not exert enough force to get the rocket ship far enough away from earth.)
2. Why do you suppose it did that? (If there is not enough thrust or force on the rocket ship, it will go up and just come right back down. Here you can discuss how enough thrust/force is needed to get beyond the gravitational pull, also a force.)
3. Did anyone observe the earth or the moon pulling the rocket ship toward it? Did it change the motion of the rocket ship? (Kids may have noticed the moon having an effect on the rocket ship's path. Discuss that this pull/force also changed the motion of the object.)

### Related Activities

Seven, six, five, four, three, two, one... blastoff! Watching a rocket take off is pretty amazing, especially when you think about how big one is—one of the Delta rockets is 23 stories high! How much power would you need to launch a rocket that big into space and how would you make sure it goes where you want it to go?