Normal Force and Tension
Contact forces push perpendicular to surfaces and pull along ropes.
About this topic
The normal force is the push of a surface perpendicular to it, balancing the part of weight pressing into the surface. It isn't always equal to weight: on a slope it is mg cos θ, and in an accelerating lift it changes. Tension is the pulling force transmitted along a rope or string.
In an ideal light rope the tension is the same throughout, and it can only pull, never push. A pulley changes the direction of the tension without changing its size. When objects are connected, they share the same acceleration, and you apply F = ma to each one, or to the whole system.
Example: two blocks of 2 kg and 3 kg hang from a pulley. The net force is the weight difference, 10 N, shared over 5 kg, giving a = 2 m/s². The tension in the string is then 24 N. Cranes, elevators, climbing ropes, suspension bridges and guitar strings all depend on tension and normal forces.
Misconception: the normal force is not a reaction to weight in the Newton's third law sense. The third-law partner of your weight is the pull of your body on Earth. The normal force arises from the surface compressing slightly.
Key ideas
- Normal force is perpendicular to the surface
- Tension pulls along a rope
- Ropes are assumed massless
Quick check
Use cases: where Normal Force and Tension helps
- Homework: review the key idea behind Normal Force and Tension before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Normal Force and Tension without notes.
- Visual learning: play with the interactive lab to see how Normal Force and Tension changes when you adjust its inputs.
- Teaching a friend: explain Normal Force and Tension in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Normal Force and Tension?
Contact forces push perpendicular to surfaces and pull along ropes.
What will I learn in Normal Force and Tension?
Normal force is perpendicular to the surface. Tension pulls along a rope. Ropes are assumed massless.
Is Normal Force and Tension part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Normal Force and Tension lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Normal Force and Tension?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.