If a car moves consistently at 80 kmh and it weighs at 600kg, is it not generating any force? since you know, a=0, am I stupid or is Newton ?
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Because speed is constant if no force is being applied. A force of zero doesn’t make a thing suddenly stop… And if you think it does, you should consider “stopped, relative to what?“
No, it is not generating any force. It has a lot of energy, but only outputs force when it is slowed down either by hitting the brakes or a wall.
It has momentum which is what you are describing. Because of friction you need to apply a small force to keep the car at constant speed.
Because force is calculated through *CHANGE* in rate and direction of the velocity (speed with direction) and not through the velocity the object already has.
What you are thinking if is momentum where P(power)= M(mass) x V(velocity).
Edit: Also as you asked: “is the car not generating any force”, force cannot be generated out of thin air if there is no other transfer of energy in the system. Meaning that if there is no combustion, propulsion, friction, or any other way for energy to transfer, there is no force acting on the car which means the car is staying a constant velocity. One more thing, it is incorrect to say force is generated because force cannot be generated but it can act on a body from another source that transfers it’s energy like I said above.
You may already know this but just in case, force can also act in a body to slow it down, for instance when you step on the breaks in a car, the breaks are apply a force to the car by causing friction which transfers kinetic energy to thermal energy(heat). What I’m saying is you can have negative forces as well which means that it’s a force acting in the opposite direction based on your perspective.
What you are missing out of your reasoning is the force of friction caused by the air, tyres and mechanics of the car. This is forces which slow you down and do act proportional to the speed. If you account for friction then in order to move at a constant speed you need to generate as much force as the friction which is a constant multiplied by the speed. If this is not the case then the car is going to accelerate depending on the difference in force between the friction and the force you are generating.
A car travelling at some speed is generating forces.
If that speed is unchanging, the sun of the forces are zero.
Take the car example. Drivetrain is pushing the car forwards with some force. The ground is pushing on the car upwards and also sticking to the tires. The air is trying to stay still and the car is pushing through it.
This means the car has to use energy, and thereby force, to maintain its speed. If you think about work being force through a distance, the car is doing work.
But the air, etc is also doing equal and opposite negative work to keep the car from accelerating
The force in the equation is not the force it will apply if it hits something. It is the force required to get that something moving (or slowed down).
Because the word force means how hard you’re pushing something, not how much energy it has.
Let’s pretend we’re on a bike instead.
The word ‘force’ means how hard you’re pushing on the pedals.
If you’re going 40 km/h (and if we pretend we live in a magic land of high school physics where friction and air resistance don’t exist) on flat land, you don’t have to pedal at all. If you’re not pushing the pedals, you’re not putting in any force and you will continue going 40 km/h. If you want to go faster, you will have to start pushing the pedals.
Newton’s first law: an object in motion will stay in motion unless a force acts upon it. An object flying through space at a constant speed has no force acting upon it.
There’s two things that may make this a bit confusing here on Earth.
First of all, any thing in motion constantly has forces acting to slow it down like air resistance and friction so, unlike in our simple scenario, you do need to apply a force to keep it moving at a constant speed.
And the second is that as soon as the object runs into anything else, it’ll exert a force on that object (causing it to slow down). So any time you try to interact with a moving object, you cause a force to happen. But the force it exerts depends on how fast it decelerates, so it’s still about acceleration. That’s why modern cars crumple in a crash- by making it take longer for the car to decelerate to 0, the force on you will be lower.
Force is defined as the rate of change of momentum. Momentum is the product of mass and velocity. Mass is a constant for a given object at this level. So force is the product of the mass and the rate of change of velocity – and rate of change of velocity is known as acceleration.
All of this stuff gets much easier when you can use calculus: a lot of the formulas to memorise in mechanics are just special cases of standard results from calculus.
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