Everyday Physics

Cross Roads Chicken

The chicken and the road joke is one of the oldest. However, very few people know that it actually dates back to the days of Isaac Newton, although it has changed somewhat over the years. Newton, in fact, used it on his colleagues at Cambridge University. Here is a reenactment of a conversation that took place in 1681:
Issac Newton: “Why did the chicken cross the road?”
John Flamsteed: “I don’t know.”
Issac Newton: “Chickens at rest tend to stay at rest, but chickens in motion tend to cross roads.”
John Flamsteed: “But what happen’s if it gets run over?”
Issac Newton: “That, my friend, is called an external force.”

This is a play on Newton’s First Law of Motion:

An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

As an example: Let’s say that a ball is lying on level ground and there is no wind or anything else to make it move. The ball does not move unless someone comes and pushes it or picks it up. When the ball is lying on the ground, in its state of rest, or non-motion,it stays that way unless someone comes and moves it. Now let us consider another ball which is moving in a straight line on the floor. There being no wind or friction(the force which opposes the motion of objects along a surface) or any other influence to make it stop, change its speed, or its direction, the ball will keep rolling on the surface at the same speed.

Motion:  means that the ball/any other object is moving, which means that it does not stay in the same place.

Non-Motion: means that the object does not move. It stays in the same place. (like me as I write this post)

Friction: when two objects touch each other, there is a force which comes into action which opposes the sliding of the two objects against each other. This is called the force of friction. When you try to slide a heavy object along the floor, you find it difficult to move it not directly because of its weight, but because of the touching of the surfaces of the floor and the object.


To summarise:

  • Newton’s First Law: Anything that is moving at constant speed in a certain direction(or is not moving at all) will maintain that speed and direction(or will remain stationary) unless something from the outside changes them.

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