A push or pull is called force in Physics.
A body is at rest if its speed is zero: it is in uniform motion if its speed is constant.
The first is called state of rest and the second one is state of uniform motion.
A force (push or pull) is always necessary to move a body from rest.
The above statement is familiar to every one.
If a body is at rest it will always be at rest unless a force acts on it.
This is Newton’s one part of First law.
The second part says that if an object is in uniform motion it will be always in uniform motion unless a force acts on it. To understand this statement some imagination needs.
We push a plate from one edge of a table to the other edge. It moves some distance and then stops. This is due to the force called friction. The table is smooth, the plate will move some what greater distance and then it will stop. We cannot avoid friction altogether. But we can infer that if there is no friction at all, then there is nothing to stop the plate from moving and it will continue to move.
However, if it slows down, there is, certainly, some force to slow it down.
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The answer to your first question is, “Objects slow down, because of some external forces, like friction.
Friction is out side force; if this out side force is absent all objects will move for ever and will never stop.
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The answer to your second question is already in the answer to your first question.
When we travel in a car, the car as well as all objects in the car is moving. If the car is moving with uniform speed, all objects in it are moving with uniform speed.
However, to keep it going with uniform speed, as per Newton’s law no force is necessary. But in practice there are always frictional forces which try to stop the uniform motion. Therefore, the engine of the car continually provides an opposite force which is equal to the frictional force. The net result is that as if there is no force acting on the car. We have to think that the engine of the car is doing nothing to keep the car in uniform motion. All that, it is doing, is to provide the opposite force of friction.
When the car is moving, we are also moving along with it. Here again the friction plays an important role.
If there were no friction between the seat and us we will not be pulled along with the bus. The friction keeps us moving along with the bus. HOWEVER, AS BEFORE, THE NET FORCE ACTING ON US IS ZERO and we are in uniform motion (constant speed).
When the brakes are applied, a force acts on the bus opposite to the direction of motion and the bus is brought to rest in certain time. But we, who are inside the bus, were moving with some speed. Unless a force acts on us to stop us from moving, we will be moving forward. That is what is happening, when we travel in the bus. However soon some external force (friction or the force which we exert on the front seat etc) acts on us and soon we are also brought to rest. If there is no friction at all, then we will be moving for ever with that speed till some force acts on it.
The conclusion is: if the net force acting on a body is zero, the body will be at rest or will be in uniform speed.”
2006-12-14 15:52:24
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answer #1
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answered by Pearlsawme 7
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No problem. The reason thing slow down and stop on earth is that gravity pulls us down into the earth, and this causes friction between you and the ground. The forc of friction slows you down.
when the car stops suddenly, you tend to continue to move in a straight line at a constant velocity, and so you do, until you are stopped by the force of friction from the seat or from hitting the dashboard or something. The same thing happens when you make a turn. If you ever have any more physics questions you can email me.
2006-12-14 13:52:06
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answer #2
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answered by Jack B. Nimble 2
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Simply because in every case there is an equal and opposite reaction which is Newton's third law. If you drop something it hits the ground because the ground pushes up with a certain force. If you drive a car and just let the car slow down to a stop, this is because the friction forces acting in direct opposition to the momentum of the car. I don't really understand your second question but I think you are asking what makes you feel a forward movement when a car stops suddenly. This is because of momentum. Momentum equals mass times velocity. When a car stops abrubtly that momentum has to go somewhere. Part of it goes into the ground in the form of heat and the other part is absorbed within the car's body and frame, while you feel a small part by moving forward.
2006-12-14 13:40:50
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answer #3
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answered by mojo2093@sbcglobal.net 5
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Question Number One
Objects slow down and stop on Earth because there are additional forces such as friction which slow things down. If the world were frictionless, when you pushed a ball, it would keep going until acted upon by another force or object. This is seen on ice, which has little friction as compared to cement. When you are rollerblading on cement you will come to a stop faster than if you were on ice because the ice has less friction and therefore keeps you moving for a longer period of time.
Question Number Two
You move forward when a car stops suddenly because for example when you are riding in a car traveling sixty miles per hour, your physical body is traveling sixty miles per hour as well. If the car comes to a sudden stop, you body will want to keep going forward at a rate of sixty miles per hour, but that is why we wear seatbelts so that we are not thrown out of cars when we get into accidents.
2006-12-14 14:41:46
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answer #4
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answered by Anonymous
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OK, I'll have pity on you, then.
Objects slow down and stop on Earth because there is friction (a force) acting against their motion. For instance, when you stop pedaling a bicycle, it slows down and eventually stops due to friction in the tires, air resistance, etc.
Q2.... well, this question, as written, is gobbledygook, but here goes...... I think you meant to ask "what force makes YOU move forward when a car stops suddenly". The answer is....no force does. If you and everything in the car are going along happily at 55mph.....and the car suddenly stops......you're STILL going 55mph so it only looks like you're pushed forward. You just haven't stopped yet. Until you slam into the dashboard, that is. So....the PHENOMENON that makes it seem as if you're moving forward is your own *inertia* - you continue to move along at the pace you had been moving while the car stops beneath you.
2006-12-14 13:41:28
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answer #5
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answered by Anonymous
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Newton's law F=ma is correct in inertial frames of reference only, that is frames moving at constant velocity and in a straight line or frames which are "still".
1) Things slow down and stop on earth because forces act on the object, like friction and gravity.
2) it is the force of inertia which arises because the frame of reference in which the phenomenon is described is not inertial anymore, a deceleration is produced. Inertia is a fictitious force.
2006-12-15 01:14:59
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answer #6
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answered by Mr. X 2
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Things slow down and stop on earth because outside forces ARE acting on them...things like friction, from the ground, air, etc.
We move forward when the car is stopping because the brakes apply an acceleration, it is opposite in the direction you are moving, or negative acceleration.
2006-12-14 13:55:18
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answer #7
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answered by Alan B 2
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q1- Friction! Objects hit the earth's atmosphere, which is matter (outside object) and slows it down. The earth, if it hits it, is obviously an outside force to stop it.
q2- momentum makes us continue to move forward when a car suddeyyl stops.
2006-12-14 13:56:22
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answer #8
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answered by climburr 1
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1. pbjects slow down because of friction. if there is no friction, then the object would move infinitely.
2. it is inertia that makes you move forward when a car stops suddenly. you were moving forward at the same speed as the car. then suddenly, the car stops, and you continue to move forward at the previous speed, because there is no outside force applied to you, so you continue moving. thus, you lurge forward!
2006-12-14 13:37:49
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answer #9
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answered by Matthew N 5
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question 1: the outside force acting on the object to slow it down is friction.
q2: momentum
2006-12-14 13:37:47
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answer #10
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answered by Kevrob_98 2
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