Science Models
Science Fair Projects

Published on Sep 16, 2023

The Pulley Catapult 194.7


The objective: We are trying to shoot a ping-pong ball 2.5 meters with a catapult and pulley.

Harry and I have been researching, investigating and learning about the are Science Fair. Are question was what is the distance that a ping pong ball can ball thrown with a catapult. When we use the pulley we will pull the weight and then release so it will release the clothespin so it will let go of of the cardboard and release the spoon so it will throw the ping pong ball 2.5 meters. Our hypothesis is going to be that the ping pong ball is going to go 2.5 meters. The reason why we were thinking of the ping pong ball to go 2.5 meters is because when we were looking at catapults on the internet we saw that one of the catapults went 2.7 meters so we thought that we can try to get are shot to go around that radius.


I am going to talk about what type of simple machines I am using to make my compound machine. The compound machine will help use less energy. I will first be talking about a lever and how you use it and how I am using it in my compound machine. Then I will talk about a pulley and how the pulley will help create the compound machine. Finally I will talk about how both machines will cooperate together to make the finishing product.

I will first talk about the lever and how it is used. There are three types of levers. The first class lever, the second class lever and the third class lever. My partner Harry and I are creating a third class lever. As with all simple machines it is used to do work. There are 3 parts to a lever. The beam which where the load is placed, the fulcrum the place the lever is able to move and the force the place you are moving the load. It helps by making it easier to move something to a different location by pushing on the edge of the beam. The way we are using the lever is going to be a catapult. This is one of the 2 parts of the compound machine.

The other simple machine that I am using is the pulley. I am using it to lift up the weight and to drop it down on the clothespin and it will release the spoon which will make the ping pong ball hopefully reach 2.5 meters. A pulley makes things easier example: you want to get a flag to a high place all you have to do is connect it to a rope and pull to raise the flag to it’s destination. There are 2 types of pulleys, a fixed pulley and a movable pulley. An example for using pulleys are for zip lining. Sometimes it is easier to use both pulleys together. These are the 2 simple machine that is going to make our compound machine.

The 2 machines that I have just talked about are the machines that are hopefully make our hypothesis of a softball going 2.5 meters true. The things we need for the experiment is wood planks, rocks, pulley ( made out of spool, rope, wood plank, a screw, rock in a plastic bag and mini hooks), a plastic spoon, a ping pong ball, a clothespin, tape, rubber bands, screws and cardboard to hold the spoon back. The way it will work is that the clothespin will be glued to a piece of wood and then the clothespin will hold one side of the card and the other side will be nailed down. There will be a pulley that will attach to the small piece of wood and when we let go of the string the clothespin will let go of the card which will release the spoon and it will throw the ping pong ball. Then it will hopefully reach the target and our experiment will succeed. This is our plan for our compound machine experiment.

I hope that Harry and I could win a prize for our experiment and these are the steps of glory to get to the prize, have fun and try our best. We will use a third class pulley (aka a catapult) for the main part of the experiment. The pulley will help by lifting and dropping the weight to the clothespin to release the spoon to throw the ping pong ball. With all the tools Harry and I will be hoping to get our experiment finished at a good mark. This is my research essay and my plan for my experiment.

This year for the science fair, I am making a catapult. This catapult consists of two simple machines, one of which is a lever. The other simple machine is the pulley. If you put the two simple machines together you get a compound machine.

The lever is a simple machine. A lever consists of a fulcrum, a load and the effort. There are 3 stages of a lever. The catapult is a stage 3 lever. If you have ever been on a see-saw, then you have used a lever. Other everyday items like scissors, crowbars, hammers and doorknobs are also levers.

The other simple machine I am using for the catapult is the pulley. There are two types of pulleys; the fixed pulley and the movable pulley. Movable pulleys are used in ziplines and cranes. Fixed pulleys are used in flagpoles and workout machines. In my catapult I am using a fixed pulley. I am using the pulley to shoot the catapult.

My catapult uses both of those simple machines. What I hope happens is that I pull the rope on the pulley and it will lift up a brick. Then when I release the rope the brick will fall on top of a clothespin. The clothespin will release a card holding the load on the lever down. Without the card holding down the load, the catapult will launch! I hope this catapult will launch a ping pong ball at least 2.5 meters.

These simple machines are small but can be very powerful. The pulley is a simple machine I am using to shoot the catapult. The lever is the spoon on the catapult. Together the two simple machines create my catapult. I can’t wait to test this out.


The materials that we used were tape, rocks, wood planks, pulley (made out of spool, rope, wood plank, a screw, rock in a plastic bag and mini hooks), ping pong ball, cardboard, plastic spoon, screws, a nail and rubber bands.


This is the procedure that we used:

1. Got a piece of wood and poked three holes for screws.

2. We got 2 rubber bands and spun them around and attached the spoon inside the rubber bands

3. we tape the clothespin to the wood. Nailed one side of the cardboard into the hole with a screw.

4. taped rock and wood plank together and put it on clothespin so it almost launches and when the rock from the pulley falls it will have enough pressure to fire the catapult.

5. Nailed a nail into a piece of wood and connected the mini hooks while they hold on to the pulley (aka the spool).

6. put the rock in the plastic bag and tied it to the rope which is hanging on the spool so when we lift the plastic bag we will let it go and it will fall on to the other rock and release the catapult.

7. We tested if our concept functioned correctly and it did after a couple tries!


We had a bit of trouble working the machine because the first 4 times it didn't work but when it worked it was a real success. Don't worry you don't have to see it not work. When we saw it launch we both thought: Oh my gosh it worked it, this is amazing! Harry and I were very proud of ourselves. We tasted success! We were so surprised that it worked after the 4 times it didn’t work. It went 2 meters and 68.5 cm

The Pulley Catapult


Our catapult functions very well! Our ping pong ball went 2 meters and 68.5cm (27inches”). That means that our hypothesis was correct. The pulley worked well with the catapult to go 2.5 meters. I learned that the catapult with the pulley worked sometimes because you had to aim very well for the rock in the bag to fall on the other rock to have enough pressure to push the clothespin to fire the catapult. The ping pong ball went farther then we expected because we were expecting it to go 2.5 meters. We made many changes to the machine because in everything you need to make a couple changes. It worked better than we expected which is a good thing. I guess I should have expected that firing then rolling will have a lot of force because first the ball will go far because of the launch but it will also have speed to roll. I don't think we need to make any changes except maybe making the catapult bigger because it is very small.







• Parker, Lewis. Simple Machines. United States of America: Perfection Learning®, 2006.

• Williams, John. Machines. England: Wayland (Publishers) Ltd, 1991.

Science Fair Project done By Harry