Laws of Motion For Kids

In the 1600s in England, Sir Isaac Newton busied himself with trying to explain things that happen on Earth and in nature. He was always asking, “Why?”

He explained gravity, motion, the motion of the planets, light, and color. He discovered so many things that he could prove by experiments and mathematics that he is often referred to as the ‘father of modern science’.

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Over the years, Newton’s ideas have been tested over and over. Scientists now agree on Newton’s ideas about motion and they have called them Newton’s Three Laws of Motion.

Newton’s First Law:

An object that is sitting at rest will stay at rest and an object that is in motion will stay in motion until a force acts upon it.

This is why astronauts can let go of a tool in space and it will stay in one spot until he grabs it. If the astronaut throws the tool, it will travel in a straight line and never stop. So, the tool will stay in one place or keep on moving in the same direction and with the same speed forever, because there is no gravity or air in space to act on the tool.

Newton’s Second Law:

F = ma The greater the force the greater the acceleration; the greater the mass, the greater the force needed to move the object; two objects with different weights (mass) will need different forces to move them and the accelerations will be different.

The formula used for Newton’s Second Law is F = ma. This is Force = mass times acceleration. You can find the acceleration by changing the formula to a = F ÷ m.

In algebra, there is a rule and it is ‘whatever is done to one side of the equation, you must do the same thing to the other side”. Try to find the formula to determine mass. You are right if you came up with m = F ÷ a

Newton’s Third Law:

For every action there is an equal and opposite reaction. Forces are always found in pairs. If the forces are equal in opposite directions, the object will not move. The forces cancel each other out so the acceleration is zero.

If one force acting in one direction is greater than the force acting in the opposite direction, the object will move. For example, if you are pulling on a rope tied to load of bricks and the bricks start to move, the force you are using is a more than the bricks are using to stay in one place.

Rockets being sent into space use Newton’s Three Laws of Motion. When the engines fire, it boosts the rocket upward against the Earth’s gravity and at the same time the explosion of fuel pushes a force out the back of the rocket.

The force forward is greater than the force backward and the rocket accelerates upwards.

Questions:

  1. What is Newton’s First Law of Motion?
  2. What is Newton’s Second Law of Motion?
  3. What is Newton’s Third Law of Motion?
  4. When in space, why does an astronaut’s hammer stay in one spot when he drops it?
  5. When a rocket’s engines ignite, what two equal forces are in action?

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Answers:

  1. Newton’s First Law of Motion: An object at rest will stay at rest and an object in motion will stay in motion unless a force acts on it.
  2. Newton’s Second Law of Motion: Force equals mass times acceleration.
  3. Newton’s Third Law of Motion: For every action, there is an opposite reaction and forces come in pairs.
  4. An astronaut’s hammer will stay in one spot because gravity and air are not acting on it.
  5. When a rocket’s engines ignite, one force is acting to push it upward into the atmosphere and one force pushes the burned fuel from the exhaust against the ground.

Physics