Year 7 Science · Unit 3 · Lesson 12

Electrostatic and Gravitational Forces

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Learning Goals

Warm Up

Real-world context

On a hot, dry day in Broken Hill in outback New South Wales, a student slides across a car seat and reaches for the metal door handle. Before her finger touches the metal, a small spark jumps across the gap and she feels a quick zap. On the same dry day, she drops her phone and it falls straight down to the floor of the car.

(a) Sliding across the seat made the student's body electrically charged. Explain how rubbing two materials together can give an object a charge.

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(b) The spark crossed a gap before her finger touched the handle, and the dropped phone fell without touching anything. What do these two events show about electrostatic and gravitational forces?

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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.

The Sun has an enormous mass, so its gravitational force reaches across the Solar System
→
Gravity is a non-contact force, so it can pull a planet without touching it
→
A planet further from the Sun feels a weaker gravitational pull
→
Earth's own gravity reaches the Moon across 384,000 km
→

Overall outcome, how can gravity keep the planets and the Moon in orbit even though it cannot push and never touches them?

Show What You Know

1. Two charged spheres are brought near each other and they push apart. A third pair is brought near each other and they pull together. What can you say about the charges on each pair? Explain using the rule for like and unlike charges.

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2. A student claims that "the electrostatic force and gravity are exactly the same thing." Evaluate this claim by giving one way the two forces are alike and one way they are different.

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Wrap Up

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

HSCScience · Year 7 Science · Unit 3 · Lesson 12 · Apply Worksheet