☯ Concept Cartoons ☯
1 Physics Earth, space and gravity 13 - Do things get lighter with height?
Have you talked about your ideas? Do you agree with any of the characters or do you think something different? Do you all have the same ideas? Here are some ways of finding out more. Talk about what you know about astronauts in the International Space Station. Do they seem lighter or heavier? What does this suggest about whether gravity changes as you go further away from the Earth? Discuss what this suggests about gravity and a hot air balloon. Hot air balloons burn propane to get off the ground. Does filling the balloon with hot gases make it lighter or heavier? If it gets heavier, how does the balloon lift off?
Here’s what a scientist might say. Did you find any evidence to support or justify these ideas? Are there any questions that you still need to answer? Gravity is a force between objects that pulls them towards each other. It is caused by the mass of the objects, so it is weaker for small objects and stronger for large objects like planets. Gravity acts no matter how far away you are from something, but it gets much weaker as the distance increases. In a hot air balloon you are slightly further from the centre of the Earth, so gravity is slightly smaller and things weigh slightly less. Some hot air balloons can go to over 20 km high, but even at that height gravity is less than 1% weaker than on the ground. Weight is a measure of the force of gravity on an object because of its mass. If gravity is weaker the weight is less, but the mass doesn’t change. Mass and weight are easily confused, but they are not the same. Make a table to show how weight and mass compare. Things to include in your table are definitions, how they are measured, units for measuring, whether, where and how they change, and when they are used.