Also, in light of the Newton's laws of motion, how is it that you can be coasting in one direction, turn the wheels of the car and then be going in exactly the opposite direction without even running the engine? Does this contradict the laws of motion?
2006-06-21 06:36:21 · 12 answers · asked by The Mog 3 in Science & Mathematics ➔ Physics
Many of you are saying friction and heat dissipation as the answer to the first part. Are you telling me that the energy of burning the gasoline to get you up to 50 mph it the same as that which would be dissipated by the brakes? - Think!
2006-06-21 13:06:58 · update #1
What would happen to the Earth when you stop the car if the car weighed as much as the Earth?
2006-06-22 13:40:52 · update #2
The KE of the moving vehicle is dissipated as heat in the brakes as the brakes use friction.
The answer to your second question is that no work has been done and therefore there has been no change in KE.
In terms of transfer of momentum, the really huge ball called the earth and the car did interact. If the car started out going West and then ended up going East, the total momentum (angular and linear) between the car and the earth must be conserved. This means that the earth was caused to change its rotation when the car turned around. Obviously, the earth is so much bigger than the car that you don't even notice the change in momentum of the earth.
2006-06-21 06:44:50 · answer #1 · answered by tbolling2 4 · 0⤊ 0⤋
Many people have correctly responded to your first question, that the kinetic (not potential - unless coasting down a hill) energy of a car is converted to heat of the brakes (as well as some energy lost in deforming the brake pads).
The second question: if I understand you correctly, you want to know how is it that by turning the wheels only the car can change directions. The answer is that an EXTERNAL force is applied - the road applies a force to turn the car. How is that possible you may ask? When you turn the wheels, the wheels create a slight sideways force on the road, essentially pushing the road. Newton's third law, that every force has an equal but opposite reaction force when a system has no net external forces acting on it, means the road is exerting a reaction force on the car. The harder the car "pushes" against the road to turn, the more the road pushes back. That force causes the car to turn.
The road is an external force to the car - but it is a "conservative" force that always acts at right angles to the car's motion - so it does not do any work on the car, neither speeding it up nor slowing it down significantly.
2006-06-21 13:05:15 · answer #2 · answered by volume_watcher 3 · 1⤊ 0⤋
When a car is moving it has kinecticenergy (of motion) rather than potential energy (of position, e.g. top of hill). When you hit the brakes, the kinetic energy is converted to heat energy due to the friction of the brakes. If you turn the steering wheel of the car, little or no kinetic energy is lost and the car moves in a new direction. If you spin a bucket of water on a rope it will have a certain constant amount of kinetic energy even though it is constantly moving in a new direction. The wheels of the car act like the rope attached to the bucket to change direction without losing energy. When the moon orbits the earth it too has a certain constant amount of kinetic energy and gravity acts similar to the rope or wheel previously mentioned in changing direction without loss of energy.
2006-06-21 07:08:32 · answer #3 · answered by Kes 7 · 0⤊ 0⤋
When a car is moving it has kinetic energy. When a car is sitting on top of a hill it has potential energy. By hitting the brakes, that kinetic energy is absorbed by the brake pads via friction and converted into heat energy.
The friction of the tires is also what provides for turning. The car has a much easier time rolling the wheels forward even when they are turned as compared to sliding them sideways across asphalt. There is also lots of force pushing to the side when a car is turning, just like if you held a pendulum in the car and turned. The force is still there, it is just being redirected.
2006-06-21 06:41:09 · answer #4 · answered by Anonymous · 0⤊ 0⤋
its been long ... i had read my last physics text 6 years ack.. nevertheless if my fundamentals are not wrong then...
when a car is running, its motion or velocity whatever u may call it because of its "Kinetic enrgy" ( and not Potential energy - which is energy due to position such as height above ground etc...). Now as the driver pushed the break pedal, it forces a restriction on the cars' speed. Now where does this energy vanish ?? This energy is transferred into heat and friction, which eventually after getting consumped bring the car to a halt.
Try touching the wheels of a car which was being driven at say 80 too 90 KM/hour and then suddenly break is applied.
Hope this clears your doubt.
Take care !!
and remember "Physics Rocks !!!"
2006-06-21 07:05:04 · answer #5 · answered by rahul_2111 1 · 1⤊ 0⤋
the other answers adequately answer the first part of your question. there is NO violation of newton's laws. ( obviously a lot of physicists would have been arguing over this right now ).
regarding your additonal remark, YES , the brakes absorb all this energy of motion and produce a LOT of heat ( again touch your brakes to find out ). YES, the brakes destroy all that energy produced by the engine that you find hard to believe. ( creating energy is a lot more difficult than removing it ! )
additonally, what the others have NOT mentioned, some of this energy of the forward moving car is translated into a different angular motion ( the leaning of the car downwards at the front ) during braking. this downward lurching is eventually absorbed by the shocks and springs with resulting heat ( touch them ).
hope your question was answered :)
2006-06-21 14:39:16 · answer #6 · answered by fullbony 4 · 0⤊ 0⤋
In terms of potential energy, nothing occurs. Potential energy relates to gravity, elasticity (i.e. a spring), electricity, or chemically. Not of mechanical motion in a way that is perpendicular to the force of gravity. Whether the car is moving along the road or at rest, the potential energy is the same as long as the distance to the center of gravity (i.e. the center of the Earth) doesn't change.
As to your second question, "An object at rest will stay at rest unless acted upon by an outside force. Conversly an object in motion will stay in motion, unless acted upon by an outside force." Since you are coasting along (you are in motion), no matter where you steer the car it will remain in motion. Some of that motion will be lost in the friction that you occur during the turning motion and friction between the car and the road. Friction is an outside force.
2006-06-21 06:53:48 · answer #7 · answered by Nate 3 · 0⤊ 0⤋
both heat energy (by friction) and also some kinetic energy that is transferred into the earth itself. In fact, if the wheels don't skid at all, some of the energy would deform the rubber tires, but most would go right into the planet, altering it's rotation (although the same energy given to the earth was taken at the moment of acceleration, so it evens out).
2016-03-27 00:00:21 · answer #8 · answered by Anonymous · 0⤊ 0⤋
A car has kinetic energy due to motion. The kinetic energy is converted into heat by brake.
2006-06-21 07:18:47 · answer #9 · answered by loni 2 · 0⤊ 0⤋
A moving car has kinetic energy. It is in motion. When you stop you have potential energy. That must be one really big hill if you can do a u turn and go back up hill. You would only get so far and gravity would pull you back down.
2006-06-21 06:43:55 · answer #10 · answered by AlphaFemale 5 · 0⤊ 0⤋