Gravity Examples in Physics

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Gravity.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Physics.

Concept Recap

The universal attractive force between any two objects with mass, decreasing with the square of distance.

Everything pulls on everything else—but only huge things (like Earth) pull noticeably.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Gravity acts between all masses everywhere — it never turns off, only weakens with distance.

Common stuck point: Gravity never 'turns off' in space—astronauts float because they're falling around Earth.

Sense of Study hint: When you see a gravity problem, identify the two masses and the distance between their centres. First, substitute m_1, m_2, and r into F = Gm_1 m_2 / r^2. Then compute the numerator and denominator separately before dividing. Finally, check your answer's units are in newtons.

Worked Examples

Example 1

easy
Calculate the gravitational force between Earth (M = 5.97 \times 10^{24} \text{ kg}) and a 1 \text{ kg} object at Earth's surface (r = 6.37 \times 10^6 \text{ m}). Use G = 6.674 \times 10^{-11} \text{ N m}^2/\text{kg}^2.

Solution

  1. 1
    Apply Newton's law of gravitation: F = \frac{GMm}{r^2}
  2. 2
    Substitute: F = \frac{6.674 \times 10^{-11} \times 5.97 \times 10^{24} \times 1}{(6.37 \times 10^6)^2}
  3. 3
    Calculate: F = \frac{3.98 \times 10^{14}}{4.06 \times 10^{13}} \approx 9.8 \text{ N}

Answer

F \approx 9.8 \text{ N}
This calculation confirms that g \approx 9.8 \text{ m/s}^2 at Earth's surface. Gravity is the attractive force between any two masses, governed by the universal law of gravitation.

Example 2

easy
A ball is dropped from rest near Earth's surface. How fast is it going after 3 \text{ seconds}? Ignore air resistance and use g = 9.8 \text{ m/s}^2.

Example 3

medium
Calculate the gravitational force between two 50 \text{ kg} masses separated by 2 \text{ m}. Use G = 6.674 \times 10^{-11} \text{ N m}^2/\text{kg}^2.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
At what height above Earth's surface would the gravitational acceleration be half of g? Earth's radius is R = 6.37 \times 10^6 \text{ m}.

Example 2

medium
What gravitational force exists between two 5 \text{ kg} masses whose centers are 2 \text{ m} apart? Use G = 6.674 \times 10^{-11} \text{ N m}^2/\text{kg}^2.
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Related Concepts

ForceMassWeight

Background Knowledge

These ideas may be useful before you work through the harder examples.

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