The Gravity Force Lab simulation from PhET lets you change the mass of two objects and the distance between them, and watch the gravitational force between them change. Force arrows show the size of the pull on each object, so you can see how mass and distance control gravity instead of just memorising a formula. It is free, runs in any browser on a phone, tablet or laptop, and it is a great fit for gravitation chapters in Tamil Nadu State Board (Samacheer Kalvi) Science and Physics.
What is the Gravity Force Lab simulation?
This interactive simulation shows two objects in space. You change the mass of each object and the distance between them, and force arrows show the gravitational pull each object feels. You can compare the two arrows to see Newton’s third law at work, and you can design your own experiments to find how force depends on mass and distance. Because it runs on HTML5, there is nothing to install, and it works on phones, tablets, Chromebooks and computers.
High school to university
Two mass controls and a distance control
Phone, tablet, Chromebook, PC
English
PhET’s learning goals include relating gravitational force to the masses and the distance between objects, explaining Newton’s third law for gravitational forces, designing experiments to derive an equation for gravitational force, and using measurements to find the universal gravitational constant.
Launch the Gravity Force Lab simulation online
Tap or click inside the player and change the masses and the distance. Use the full-screen button in the player for a bigger view.
Credit: University of Colorado Boulder
How to use the Gravity Force Lab simulation, step by step
- Predict first. Before changing anything, say what you think will happen to the force.
- Change one mass. Make one object heavier and watch both force arrows grow.
- Change the distance. Move the objects farther apart and see the force shrink quickly.
- Compare the two arrows. Even when the masses are very different, the two forces are equal in size and opposite in direction.
- Design an experiment. Change only one variable at a time and record the force to find the pattern yourself.
Tip for students: double the distance and check the force. If it becomes one quarter, you have found the inverse square law.
The idea behind the simulation: F = G m₁ m₂ ÷ r²
F = G × m₁ × m₂ ÷ r²
Here F is the gravitational force in newtons (N), m₁ and m₂ are the masses in kilograms (kg), r is the distance between their centres in metres and G is the universal gravitational constant, about 6.674 × 10−11 N·m²/kg². Gravity always attracts. The force grows with mass and falls with the square of the distance.
Worked example: Two objects of 1000 kg and 500 kg are 10 m apart. The force is F = 6.674 × 10−11 × 1000 × 500 ÷ 10² ≈ 3.3 × 10−7 N. Each object feels this same force. It is tiny, which is why we only notice gravity when one of the masses is as huge as a planet.
Gravity key terms explained
These are the words you will meet while using the Gravity Force Lab simulation, with simple meanings.
Gravitational force
The attractive force between any two objects that have mass.
Mass
The amount of matter in an object. Measured in kilograms (kg).
Distance (r)
The gap between the centres of the two objects. Measured in metres (m).
Universal gravitational constant (G)
A fixed number that sets how strong gravity is everywhere in the universe.
Inverse square law
When the distance doubles, the force becomes one quarter. When the distance triples, it becomes one ninth.
Newton’s third law
If object A pulls on object B, then B pulls on A with an equal force in the opposite direction.
Force pair
The two equal and opposite forces that two objects exert on each other.
Centre of mass
The point where an object’s mass can be treated as concentrated. Distance r is measured between these points.
Common mistakes: Thinking the heavier object pulls harder than the lighter one (the two forces are always equal), using the gap between surfaces instead of the distance between centres, and forgetting to square the distance.
Try the gravitational force calculator (practice what you explore)
Enter two masses and the distance between them to see the gravitational force. Then tap a “what if” button to see how the change affects the result.
What happens to the force when you change a variable
| Change | Effect on gravitational force |
|---|---|
| One mass doubled | Force doubles |
| Both masses doubled | Force becomes four times larger |
| Distance doubled | Force becomes one quarter |
| Distance halved | Force becomes four times larger |
| Distance tripled | Force becomes one ninth |
Classroom activities for teachers
The Gravity Force Lab simulation fits a single 40-minute period.
- Predict and test (10 min): students write a prediction for each change, then check it in the simulation.
- Find the pattern (10 min): students change one variable at a time, record the force and discover the inverse square law.
- Force pairs (10 min): compare the two force arrows for very different masses and explain Newton’s third law.
- Exit ticket (10 min): students explain in two sentences why we do not feel the gravity of everyday objects.
Looking for the matching chapters? Browse the Science and Physics books on TN SchoolBooks and download the Samacheer Kalvi PDFs, then use this simulation to make the gravitation lessons visual. More free science simulations and textbook PDFs are on the home page.
Quick quiz: test your understanding of gravitational force
Score: 0 / 5
Gravity Force Lab simulation: frequently asked questions
Is the Gravity Force Lab simulation free?
Yes. PhET simulations are free to run online in a browser. Check PhET’s licensing page for reuse terms.
Does it work on a mobile phone?
Yes. It is built with HTML5 and works on phones, tablets and Chromebooks. Use landscape mode or the player’s full-screen button for a bigger view.
What does the inverse square law mean?
It means the force falls with the square of the distance. If you double the distance between two objects, the gravitational force becomes one quarter of its old value.
Do both objects feel the same gravitational force?
Yes. By Newton’s third law, the two objects pull on each other with equal force in opposite directions, even if their masses are very different.
The Gravity Force Lab simulation turns an invisible force into something you can adjust, measure and see. Explore it, take the quiz above, and keep experimenting until predicting the force feels easy.