Does kinetic friction always oppose the direction of motion?

No it does not. In some cases friction can cause motion. To illustrate this we will consider a body M1 of length L placed on a frictionless surface and a smaller body M2 placed on top of M1 on the leftmost edge of it. The coefficient of kinetic friction between M1 and M is μk and the positive direction of motion is to the right. If we start applying a force F on M2 of big enough magnitude, it will start moving on top of M1 towards the rightmost edge of it. The forces acting on M1 on the x-axis will be the positive force F we are applying and a negative frictional force FF12 applied on M2 by M1.. According to Newton's Third Law, there must be an opposite - equal in magnitude and opposite in direction - force acting on M1 by M2, ie the reaction of FF12. This positive frictional force, FF21, is the only force acting on M1 on the x-axis, and therefore causes it to move towards the right.

SA
Answered by Stella A. Physics tutor

4794 Views

See similar Physics GCSE tutors

Related Physics GCSE answers

All answers ▸

Which type of electromagnetic radiation has the longest wavelength?


What's the difference between elastic and inelastic collisions ?


What is refraction?


In an isolated container contains 1kg of ice at 0 oC. 1kg of warm water (323K) is poured into the container. How much ice (in kgs) remains after the system returns to thermal equilibrium? (by the end of the process?)


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning