Newton’s Laws of Motion

Newton’s first law of motion states that an object at rest stays at rest and an object in motion stays in motion unless acted upon by an outside force. Take a bowl of water for instance; if it is at rest and nothing is prompting it to move the water will stay at rest. This does not mean however, that no forces are acting upon it. Gravity and the normal force are both acting upon the water, but are balanced. If you were to remove the normal force, the bowl with the water would fall to the ground.

When you stir the water you apply an outside force, causing the water to move. Unlike when the water was at rest, the forces are now unbalanced. Gravity and the normal force are still there, but are now accompanied by the force you are applying when you stir the water. In order for the water to be still, you would need to apply an equal force in the opposite direction to stop the stirring and balance the forces.  

When you stop stirring, the water will continue to move, but will eventually stop. This is because there is sliding friction between the water and the sides of the bowl. As well as a smaller amount of friction between the water’s surface and the air. Sliding friction is a type of kinetic friction that slows down an object as it slides. Sliding friction is caused by the roughness of two objects. If you apply more force the water will move for a longer amount of time, but the friction will always stop it eventually.

Newton’s second law of motion says that an object acted upon by a force will accelerate in that direction. In mathematical terms, acceleration=net force/mass or net force=acceleration x mass. Meaning the more force and the less mass the greater the acceleration. If you were to stir the water in the bowl at a faster rate, applying more force, the water would accelerate faster. If you were to stir the water at a slower rate it would move slower.

Newton’s third law of motion states that for every action there is an equal but opposite reaction. If you were to squeeze a water balloon up against a wall or in your hand you would see the balloon stretch. This is because as you push on the balloon, the balloon pushes on the wall, and the wall pushes back on the balloon. Pushing on the balloon is the action and the reaction is wall pushing back on the balloon.