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This week we’re exploring the power of gravity and how you can change the effects of gravity using simple machines.

Gravity

Have you ever wondered why we walk on the ground instead of floating around, and why things fall when we drop them? It’s all because of gravity. 

Gravity is the theory of how objects are pulled toward each other, as described in this TedX video. Just as the Earth pulls us down toward it, we also pull the Earth to us. 

However, we are very small compared to the Earth, so we only pull the Earth a tiny bit. The Earth is gigantic compared to us, so its pull is enough to keep our feet stuck to the ground and shrink our spine so that we’re shorter at night than we are in the morning, as explained in this video about the concept of gravity. This means that if we were on a planet of a different size, gravity would pull us down a different amount. You can find out how gravity changes your weight on other planets here, and see how gravity affects us on Earth and in space in these online games at Legends of Learning (requires creating a free account to play).

To get a better understanding of how gravity works on Earth, you can follow instructions to hear the rhythm of weights falling. If you’re feeling ambitious, you can measure how fast things fall. You can also follow the Museum of Science and Industry’s Science at Home project to investigate how toilets use gravity to flush away waste. This project is also available in Spanish.

You’ve probably heard about how gravity makes feathers and bowling balls fall to the ground at the same time and found it hard to believe. After all, one is so much heavier than the other. You can test the falling feather theory at home (be warned, it requires a lot of equipment), or watch NASA's recorded vacuum drop experiment. 

Simple Machines

Gravity might be a powerful force pulling things down, but we can fight gravity to push things up if we are strong enough. Our own bodies are powerful enough to lift a book, but we are not powerful enough to lift a car. However, we can reduce the amount of force we need to lift heavy things if we use simple machines like ramps, levers, and pulleys. 

Ramps
A ramp is a flat surface placed at an angle that helps you move things from a low place to a high place. For example, Jessi and Squeaks use ramps to move heavy books up the stairs into their house. Ramps are also called inclined planes. As we learn from Elmo and Abby, a simple cardboard tube can act as a ramp. 

You can experiment with different kinds of ramps at different heights and lengths to make it easier to pull something up the ramp or push something down the ramp faster. Some examples of ramps you see every day are playground slides and mountain roads. On a rainy day when you can’t test gravity at the playground, try online games to play with gravity, force, and motion.

Levers
A lever is a plank or beam that pivots on a fulcrum. A fulcrum is the thing that sits under the plank and lifts one end higher. Levers help us lift or move heavy things, as Jessi and Squeaks find when they use a stick and a rock to turn over boulders. You can experiment with the length of the plank and where you put the fulcrum to see if it makes it easier to lift things. Some examples of levers you may see everyday are seesaws, chopsticks, fishing-lines, oars, wheelbarrows, and shovels. Balancing Act lets you play with items on a teeter totter to learn about balance.  

Pulleys
A pulley is made up of a wheel with a groove in it, and a rope in the groove. One end of the rope is connected to a heavy object, and you pull on the other end to lift the heavy object to a high place, like this heavy telescope was lifted to the top of a tower. Pulleys work by redirecting the force needed to lift things. This means that you’re not working against gravity to push things up, but you’re using gravity to help you pull the rope down. Watch a video that explains pulleys, and learn how to build a pulley out of things you might have around the house. Try adding more wheels and ropes to the pulley--will this make it easier to lift things?

If you don’t have any building materials to make ramps, levers, and pulleys, you can still run the same experiments with the Simple Machines game, where you help a robot collect objects from around the Museum of Science and Industry (this game requires Flash to operate). 

We use simple machines every day to do lots of things. Bicycles use gears and chains to transform a little bit of effort from your pedaling into a lot of forward motion. Garlic crushers use levers to help you squish garlic into tiny bits. What other simple machines do you use in your everyday life?

Complex Machines

Can you combine all of these simple machines into a Rube Goldberg machine? A Rube Goldberg machine is a very complicated device that uses lots of different contraptions to do something simple, like turn on a light. 

First, think of a task that you need to do, like passing the salt during dinner. Next, experiment with different ways you can use a simple machine to complete this task, like this team tries different ideas to clean a messy room. Combine your ideas to create a masterpiece, as shown in this music video by OK Go. 

The Museum of Science and Industry has a Rube Goldberg project for hot summer days when you don’t even want to get up for a drink of water. 

Scientist of the Week

Melonee Wise is a robot ninja who makes robots that play fetch. Melonee is the CEO and cofounder of Fetch Robotics, a company that builds robots to help move things around giant warehouses and factories. 

Melonee says that engineering is “one of the most creative pursuits around” because you need to think creatively to solve tricky problems. As a child, she used her creativity to build machines out of Lego blocks.  

Although Melonee studied Physics Engineering and Mechanical Engineering at the University of Illinois at Urbana-Champaign, she says that you can learn about engineering outside of school by experimenting and solving problems. 

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We’d love to see the results of your experiments. Remember to take a video of your Rube Goldberg machine in action and share it with us on Instagram or Twitter at @skokielibrary.

Written by Michelle and Pam.