Gravity and Weight 17 November 2018 Objectives: To describe the difference between mass and weight on the surface of planets. To describe the gravitational forces between planets.

Starter (5 mins) Place a labelled 1 kg metal mass in front of the students and ask them to describe exactly what it is and the properties it has. Key points: particles (atoms), physical properties and the forces acting on the block

What is gravity? Gravity is an attractive force that acts between all objects that have mass. The size of the force depends on the masses of the objects. Earth’s gravity Satellite’s gravity All objects produce a gravitational force. This is very large for huge masses such as planets. When you jump, the gravitational force of the Earth pulls you down. Your gravitational force also pulls the Earth towards you, but you don’t notice it because the Earth is too heavy to be visibly affected by your gravity.

What are mass and weight? Mass is the amount of matter in an object and is measured in kilograms. Mass is not a force. An object, such as this satellite, has the same mass at any point in the Universe. Weight is a force and is caused by the pull of gravity acting on a mass. Photo credit: © 2007 Jupiterimages Corporation Weight is measured in newtons and has both magnitude and direction. An object’s weight changes depending on where it is in the Universe.

Mass and weight on the Moon The force of gravity on the Moon is only one-sixth of that on Earth because the Moon has a much smaller mass. Any object on the Moon weighs one-sixth of the amount it would weigh on Earth. Astronauts can jump up 20 feet on the Moon due to there being such a low gravitational force. Photo credit: © 2008 Jupiterimages Corporation However, the astronaut still has the same mass – they just weigh less because gravity is weaker.

Sheet Can complete worksheet questions to check progress

Practical Pupils can measure their mass and then calculate their weight on each planet

Practical My mass is ………… kg Name of planet Gravitational strength (N/kg) My weight on this planet (N) Mercury 3.8 Venus 8.8 Earth 9.8 Mars Jupiter 25 Saturn 10.4 Uranus Neptune 13.8

Mass and weight on different planets Worksheet 1 accompanies this slide. It provides further practice at calculating weights in different gravitational fields.

Plenary (10 mins) Show the students the behaviour of ’toys in space‘ and have them compare their behaviour to those on Earth using the knowledge gained this lesson. www.nasa.gov/audience/foreducators/microgravity/home/toys-in-space.html