Newton's First Law of Motion - why do I need to keep my foot on the accelerator?

Question

When driving my car at a constant velocity on a flat road i find it necessary to to keep my foot on the cars accelerator. Is newtons first law being broken? Why?

Is it something to do with the extra force needed to overcome drag or other factors, so that the car has a... i don't know, equal force (im really not sure about this).... It has no net force so therefore continues at constant velocity? Clearly i don't know what im talking about.

Any help explaining is appreciated. :)

Answer 1

This is a good example of why the word “accelerator” is a bad choice. The throttle does not control the acceleration of the car, but the power of the engine. (power = velocity · force)

As other answers have already stated: in the real world, you cannot sustain speed without the power of the engine. The power is not used to accelerate the car, but to overcome friction (also in the engine), drag, etc. Going uphill up will need more power than downhill.

So what about Newton's First Law? Read it this way: if the sum(!) of all forces is zero, the car will move at constant velocity. The force of the engine has to compensate the forces of drag, friction, and gravity, for the sum to be zero.

According to Newton's Second Law of Motion: If the sum of forces is unequal zero, there will be an acceleration. It may be positive or negative.

Answer 2

If there were no such thing as friction or wind resistance, then indeed you wouldn't burn gas at constant cruising speed on the level. But there is, so you do.

Answer 3

There is force from the thrust of the car's engine propelling you forward. But if you suddenly shift into neutral, the car will slow down and eventually stop. Why? For the same reason cars are made lighter and aerodynamically sound.

Rockets in space don't need to step on the gas because in space it's essentially weightless. On Earth, gravity pulls the weight of the car down. The heavier the car and its contents, the harder the pull.

Also, wind resistance has a say. It's a lot easier to accelerate in a tailwind than a head wind.

Answer 4

yea it because of frictional forces which is the opposite of the movement of ur car...

so basicly u accelerate but u are in constant velocity because the frictional forces in diferent direction cancels it out...  

Answer 5

Anytime the car is moving, it experiences drag from wind resistance and from the friction of the tires on the pavement (or dirt/gravel/cobblestone/whatever). In addition to that, all of the moving parts in the engine cause friction which adds more drag from the inside.

Answer 6

there is no situation in which an object is moving in a frictionless environment. you have to keep your foot down because of friction and drag.

Answer 7

Well the first law says"An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force"

Your car is experiencing unbalanced forces such as

1 - Gear wheels

2-Atmospheric Air

Answer 8

I think you're closer than you think in your guess.

"Overcoming drag" sums it up in a nutshell. In the case of a car, there are three main contributors to drag (or in Newton-speak, an unbalanced force working to slow the car down):

- Rolling resistance of the tires

- Friction in the axles and drivetrain

- Air resistance

Without some power from the engine to overcome these forces, your car will slow down and eventually stop.

If you've ever seen one of those solar endurance cars built for competition, you'll notice that 1) their tires are extremely hard rubber, for less rolling resistance, 2) their axles ride on extremely low-friction bearings, and 3) they are very aerodynamic (and not comfortable to sit in!). All of that means they require very little power to maintain a given speed on flat ground.