# Relation between velocity and force

by animespt
Tags: force, relation, velocity
 P: 3 Ok, so heres the question. To make a car move, we need a force, however, the velocity of the car is related to force? By example, we made a force to make the car start moving and the car started moving with a velocity of 10m/s. Then later the car has a velocity of 20m/s. So, the increase of the velocity is caused by a bigger force pushing the car? Cos, i do know that if the car is moving, then it has the tendence to keep moving with a constant velocity, it can only be stoped with a force in the opposite way to make it stop, so to make it go faster, then theres a force pushing it to go faster?
 Emeritus Sci Advisor PF Gold P: 9,789 Welcome to Physics Forums. I'm not sure that I entirely understand your question, but yes, to change an body's velocity there must be a net force acting on that body.
 P: 3 ok, and whats the formula to find the force used in the increase of velocity? thanks by the answer gived by the way.
Mentor
P: 28,449

## Relation between velocity and force

Er... F=ma!

Zz.
 P: 3 but thats when a = v^2/r in a circular movement. and on a rectilineous movement?
Emeritus
PF Gold
P: 9,789
 Quote by animespt but thats when a = v^2/r in a circular movement. and on a rectilineous movement?
Newton's second law can be applied to any classical motion, when rectilinear or curvilinear.

I just want to make sure that you know that the equation for acceleration that you quoted is only valid for circular motion.
Mentor
P: 28,449
 Quote by animespt but thats when a = v^2/r in a circular movement. and on a rectilineous movement?
What?

Since when is F=ma only valid in circular motion?

Zz.
 Mentor P: 21,897 I also want to make sure you understand how Newton's first law applies to a car: the car decelerates when you take your foot off the gas pedal because there are forces acting to decelerate it. And when you add more gas, the car accelerates to a new equilbrium with its opposing forces. Force has no direct relationship with velocity, only acceleration.

 Related Discussions Introductory Physics Homework 9 Introductory Physics Homework 1 Classical Physics 3 Mechanical Engineering 4 Introductory Physics Homework 16