Jon Chase explains that the mass of an object is constant but its weight depends on the gravitational force. This force is higher on more massive planets and he would weigh more on Jupiter than on Earth. He uses a fairground ride to simulate the feeling of lower and higher gravitational forces. He explains that gravity is the force that keeps spacecraft and moons in orbit around planets and planets around stars. Astronauts in the International Space Station experience weightlessness because they are in orbit and constantly falling towards Earth. Teacher notes: Discuss the difference between mass and weight. Students could compare the weight of 1 kg mass on different planets. The class could give their own examples of feeling lighter or heavier and describe the forces involved. Introduce the idea of gravitational force causing lighter objects to orbit heavier ones, perhaps using concept cartoons or true/false statements.