Gravity is the invisible force of attraction that makes our feet stick to the ground and makes us come back down when we jump up. On Earth, we may be able to temporarily jump or throw a ball into the air, but gravity will bring us back down. In this activity, your child will use a combination of simple machines, a lever and an axle, to build a catapult, and then use the catapult to conduct a simple investigation showing that when things go up, gravity will bring them back down. WATCH THE VIDEO
Materials
Empty tissue box
Scissors
Two pencils
Several rubber bands
Pipe cleaner or a large paper clip
Plastic spoon
Tape
Small rubber ball or pompom balls
Directions
1 Before you begin, start a conversation with your child about gravity — where has he noticed gravity in action? For example, ask, “If you jump up in the air, do you always come back down? If you throw a ball into the air, does it always come back down?” Based on previous experience with gravity, ask your child to make a prediction: Will a ball launched into the air with a catapult come back to the ground? Why or why not?
2 Begin building the catapult. Create a large opening in the tissue box by enlarging the current tissue opening.
3 Cross two pencils (into a "t" shape) and connect them together with some rubber bands. The horizontal (side-to-side) pencil should be connected to the lower part of the perpendicular (up and down) pencil. The perpendicular pencil will be the launch for the catapult.
4 Make three holes; two on each side of the catapult towards the top and one on the front near the bottom.
5 Cut two rubber bands open and tie them to together so that you have one long band. Attach one end to a pipe cleaner or large paper clip.
6 Feed the pipe cleaner/paper clip through the hole at the bottom of the catapult in the front so that it anchors the rubber band.
7 Insert the pencils so that the horizontal pencil pokes through the side holes.
8 Create a landing pad by using tape or rubber bands to attach the plastic spoon onto the top part of the pencil, covering the eraser.
9 Attach the loose end of the rubber band to the spoon and pencil.
10 Pull back the spoon and attached pencil so that the spoon is facing upward. Place a ball on the spoon. Carefully let go of the spoon so that your hand does not block its movement. The ball should fly through the air for a distance and then fall down to the ground.
11 Launch the ball several times. Does it always come back down to the ground after a distance of flying? Yes! The force of gravity is pulling the ball back down to earth.