Describe solid friction and the heating it can produce
Identify contact friction, distinguish grip from sliding resistance and explain rubbing-induced heating.
Exam scope and assessment notes
Core and Extended · Physics 0625, 2026–2028, section 1.5.1. Core covers deformation, load–extension experiments and graph interpretation, collinear resultants, constant velocity, friction and drag. Numerical spring constants, the limit of proportionality, F = ma and the specified circular-motion comparisons are Supplement work in separately labelled Extended lessons. Written practice is self-checked; cumulative assessment, supervised practical experience and human subject-teacher review remain pending.
Before you begin
- Identify surfaces in contact.
- Calculate simple opposed-force resultants.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which pair can produce solid friction?
What you will learn
- Describe friction between solid surfaces.
- Explain how friction can impede sliding and produce heating.
Contact can resist relative sliding
Solid friction acts between contacting surfaces and can impede their relative motion. On a crate sliding right across a stationary floor, the floor's friction on the crate is leftward. With a 25 N rightward pull and 15 N leftward friction, the horizontal resultant is 10 N right.
Static friction can prevent attempted slipping before surfaces slide. Its value is not automatically the same fixed number as a sliding-friction force. In a stated model with available static friction up to 20 N, a 12 N horizontal push on a resting crate can be balanced by 12 N friction. No coefficient formula is needed for this syllabus requirement.
Friction can help and can warm surfaces
Rubbing hands or applying brakes can raise the temperature of contacting parts. Motion-related energy is transferred into internal energy of the interacting materials; the force does not mean heat is a substance created from nothing. The physical effects include resistance to sliding and heating.
Grip can be useful: walking requires friction to prevent slipping and can involve a forward friction force on the foot. Thus friction opposes relative sliding or its tendency, not necessarily the object's overall direction of travel in every situation. Name the chosen body and contact pair before assigning a direction.
Pause and explain
A resting crate has a 12 N push, balanced within an available static-friction limit of 20 N. What is friction?
Worked example
A crate slides right while pulled by 25 N right and opposed by 15 N floor friction. Find resultant and name a possible thermal effect.
Show the worked solution
- Select forces on the crate.
- 25 − 15 = 10 N right.
- The contacting surfaces can warm during sliding.
Answer 10 N right; friction can heat the contacting surfaces.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A sliding crate is pulled 25 N right against 15 N leftward floor friction. Find its resultant.
Give me a hint
Add the forces on the crate with a chosen sign direction.
Compare my reasoning
- Choose right positive.
- 25 − 15 = 10 N.
- The resultant is rightward.
10 N right.
Look for these in your work
- Identify the contact resistance.
- State resultant direction.
A crate rests under a 12 N push on a surface able to supply up to 20 N static friction. Find the balancing friction and explain whether the maximum is used.
Give me a hint
The actual balanced force depends on the push, not only the stated limit.
Compare my reasoning
- Resultant must be zero in the given resting setup.
- Friction is 12 N opposite the push.
- Twelve is below the 20 N maximum.
12 N opposite the push; the maximum is not used.
Look for these in your work
- Balance the actual push.
- Distinguish a force from its limit.
Brakes warm while slowing a bicycle, yet shoe–ground friction helps a person walk. Explain why both can be friction effects.
Give me a hint
Identify the contacting surfaces and their relative-sliding tendency.
Compare my reasoning
- Brake contact resists relative sliding and transfers energy into warming parts.
- Shoe–ground grip can prevent slipping and help propel the walker.
- Friction is not universally opposite the body's overall travel direction.
Brake friction resists sliding and heats parts; grip prevents slipping and can assist walking.
Look for these in your work
- Connect heating to contact.
- Explain the useful-grip case.
Common mistakes
- Friction is a contact interaction.
- Static friction is not always at its maximum.
- Grip can assist motion rather than always acting backwards.
What can you explain now?
A 12 N push is balanced by static friction. Must friction equal a stated maximum of 20 N?
Compare with the explanation
No; it is 12 N in this balanced situation.
A maximum available value is not the force required for every smaller push.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain one friction-heating example and one useful-grip example, naming both surfaces.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.