Year 7 Science · Unit 3 · Lesson 1

What Is a Force? Contact and Non-Contact

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Learning Goals

Warm Up

Real-world context

Australian astronaut Katherine Bennell-Pegg completed training with NASA in 2024 as the first Australian to qualify as a mission specialist. Aboard the International Space Station (ISS), which orbits Earth at about 400 km altitude, astronauts appear to float freely. Objects released inside the cabin hang in mid-air. Yet the ISS and everyone inside it is travelling at roughly 7.7 km/s relative to Earth's surface.

(a) An astronaut in the ISS releases a water droplet. Which forces are absent for the droplet at that moment — and why? (Hint: think about what the droplet is not touching.)

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(b) Which non-contact force is still acting on the water droplet inside the ISS? How do you know it is still acting?

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Your Turn

Because… chain

Fill in the missing effects in the boxes below. Each cause leads to the next step in the chain. Then write the overall outcome at the bottom.

Earth's gravity pulls the Moon toward it — a non-contact force acting across 384,000 km
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The Moon's sideways speed and gravity's inward pull are balanced just right
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The Moon keeps "falling toward" Earth but keeps missing because it moves sideways so fast
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Human-made satellites use the same principle as the Moon's orbit
→

Overall outcome — why can gravity keep the Moon and satellites in orbit even though it cannot "push"?

Show What You Know

1. Name the four fundamental forces that underlie all forces in the universe. Which two are most important for everyday Year 7 science? Explain why.

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2. A student claims that "contact forces are somehow more real than non-contact forces because you can feel them." Evaluate this claim using two examples from this lesson.

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Wrap Up

In one sentence, what was the main idea of this lesson?

HSCScience · Year 7 Science · Unit 3 · Lesson 1 · Apply Worksheet