Engineering today Why do things move … and stop moving?


In 1686, Isaac Newton wrote Mathematical Principles. In this book, he looked at the reason for movement. He discovered three important laws of motion. In this article, we look at each law, then we ask: How do the laws apply in everyday life?


Newton’s first law is about starting movement and continuing movement. An object moves if a driving force pushes it or pulls it. It continues to move at the same speed if no force acts on it. So, a car moves if the engine pushes it ... or, sometimes, you need a friend!


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Newton’s second law is about acceleration and deceleration. An object accelerates if the force increases. If the force is in the opposite direction, the object slows down or stops. So, a car goes faster with more power from the engine.


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Newton’s third law is about action and reaction. Every action causes an equal and opposite reaction. If a car hits a wall, the wall pushes back. It does, really! It pushes back against the car, and the car is damaged.


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We cannot apply the first law in everyday life exactly. Firstly, Newton says: ‘An object doesn’t move if no force acts on it.’ But gravity pulls all objects on Earth. Secondly, he says: ‘If no force acts on an object, it continues to move.’ But all moving bodies experience friction from the air and from other objects, like the ground. Engineers must add gravity and friction into all their calculations.


We can write Newton’s second law as F = m x a. In this equation, F is force, m is mass, or weight, and a is acceleration. So, a large mass at a slow speed produces a large force. A small mass with lots of acceleration also produces a large force.


Newton’s third law is the basis of motion for engineers. A rocket, for example, moves up into space because it pushes down on the exhaust gases, and the exhaust gases push back.


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Isaac Newton was born on 25th


December,


1643 in England. He studied Maths, Physics and Astronomy at Cambridge University. He became a university teacher and taught Mathematics for many years at Cambridge. Newton died in 1727 in London.


Grammar for reading: Understanding sentences with if Subject


Verb If a car


An object moves hits


Extra information a wall ,


Subject


Verb


if a driving force pushes the wall


pushes


Extra information it …


back.


Some sentences have two actions and the word if. The word can come in the middle or at the beginning of the sentence.


Find and underline the subject of each action in if sentences. It will help you to understand the relationship between the actions.


Find all the if sentences in the text. Underline the two subjects in each case. Grammar reference pages 190–191 69


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