Year 7 Science · Unit 3 · Lesson 2
Challenge Worksheet
Learning Goals
Explain it to a Year 4 student
Imagine your younger cousin has never heard of weightlessness or orbits. They ask: "If gravity is real, why do astronauts float in the ISS?" Use the sentence starters below to write a clear explanation. You may use everyday examples — but your explanation must be scientifically accurate using what you have learned.
Starter 1: "The basic idea of weightlessness in orbit is NOT that gravity disappears — it's that..."
Starter 2: "A good everyday example that shows this idea is..."
Starter 3: "The reason the ISS keeps going around Earth without falling down is..."
Starter 4: "One thing people often get confused about is that 'no weight' means 'no gravity' — but actually..."
1. Australian astronaut Katherine Bennell-Pegg (mass 60 kg) is training for a future ISS mission. (a) Calculate her weight on Earth (g = 9.8 N/kg). (b) Calculate her weight on the Moon (g = 1.6 N/kg). (c) Once aboard the ISS at 400 km altitude, gravity is approximately 8.7 N/kg. Calculate her weight there. Why does she still feel weightless despite this result?
2. A science fiction film shows an astronaut floating in a spaceship far from any planet. Another character says "That's because there's no gravity out here." Evaluate this explanation: what is correct about it, what is misleading, and what is the more accurate scientific explanation?
Wrap Up
In one sentence, what was the main idea of this lesson?