Mechanics and Motion

Motion is one of the key topics in physics. Everything in the universe moves. It might only be a small amount of movement and very very slow, but movement does happen. Don't forget that even if you appear to be standing still, the Earth is moving around the Sun, and the Sun is moving around our galaxy. The movement never stops. Motion is one part of what physicists call mechanics. Over the years, scientists have discovered several rules or laws that explain motion and the causes of changes in motion. There are also special laws when you reach the speed of light or when physicists look at very small things like atoms.

Speed it Up, Slow it Down

The physics of motion is all about forces. Forces need to act upon an object to get it moving, or to change its motion. Changes in motion won't just happen on their own. So how is all of this motion measured? Physicists use some basic terms when they look at motion. How fast an object moves, its speed or Velocity, can be influenced by forces. (Note: Even though the terms 'speed' and 'velocity' are often used at the same time, they actually have different meanings.)

Acceleration is a twist on the idea of velocity. Acceleration is a measure of how much the velocity of an object changes in a certain time (usually in one second). Velocities could either increase or decrease over time. Mass is another big idea in motion. Mass is the amount of something there is, and is measured in grams (or kilograms). A car has a greater mass than a baseball.

Simple and Complex Movement

There are two main ideas when you study mechanics. The first idea is that there are simple movements, such as if you're moving in a straight line, or if two objects are moving towards each other in a straight line. The simplest movement would be objects moving at constant velocity. Slightly more complicated studies would look at objects that speed up or slow down, where forces have to be acting.

There are also more complex movements when an object's direction is changing. These would involve curved movements such as circular motion, or the motion of a ball being thrown through the air. For such complex motions to occur, forces must also be acting, but at angles to the movement.

In order to really understand motion, you have to think about forces, acceleration, energy, work, and mass. These are all a part of mechanics.

Motion Glossary and Terms

 

Motion Glossary and Terms

Acceleration - Acceleration is the measurement of the change in an object's velocity. It is equal to the change in velocity over the change in time. Acceleration is a vector. 

Collision - A collision in physics occurs when any two objects bump into each other. 

Displacement - In physics, displacement refers to an object's overall change in position. It is a vector quantity.

 Energy - Energy is the ability to do work. The standard unit of measure for energy is the joule. 

First law of motion - The first law of motion states that any object in motion will continue to move in the same direction and speed unless external forces act on it.

 Force - Force is the measurement of a push or pull on an object. Force is a vector measured in newtons.

 Friction - Friction is the resistance of motion when one object rubs against another. It is a force and is measured in newtons.

Gravity - Gravity is a force caused when the mass of physical bodies attract each other. On Earth gravity pulls at objects with an acceleration of 9.8 m/s2. 

Impulse - An impulse is a change in momentum. 

Joule - The joule is the standard unit of measure for energy and work. 

Kinetic energy - Kinetic energy is the energy an object has due to its motion. It is a scalar quantity calculated using the formula KE = ½ * m * v2, where m = mass and v = velocity.

Mass - Mass is a measurement of how much matter is in an object. It is usually measured in kilograms. 

Momentum - Momentum is a measurement of mass in motion. Momentum is equal to the mass times the velocity of an object. It is a vector measured in newton-seconds. 

Newton - The newton is the standard unit of measure for force. Pascal - The pascal is the standard unit of measure for pressure. 

Potential energy - Potential energy is the energy stored by an object due to its state or position. It is measured in joules. Power - Power is a measurement of the rate at which energy is used. Power is calculated by dividing work over time. The standard unit for power is the watt. 

Pressure - Pressure is the force over a given area. Pressure is measured in pascals. 

Scalar - A scalar is a measurement that only measures the magnitude. Unlike a vector, a scalar does not have direction. Second law of motion - The second law of motion states that the greater the mass of an object, the more force it will take to accelerate the object. 

Simple machine - A simple machine is a basic mechanical device for applying a force and doing work. Some examples of simple machines include the lever, pulley, inclined plane, wedge, and screw. 

Speed - Speed is the measurement of how fast on object moves relative to a reference point. It is a scalar quantity measured by distance over time. 

Third law of motion - The third law of motion states that for every action there is an equal and opposite reaction. 

Vector - A vector is a quantity that has both a magnitude and a direction. 

Velocity - Velocity is the rate of change in an object's position. Velocity is a vector quantity. The magnitude of velocity is the object's speed. 

Watt - The watt is the standard unit of measure for power. Weight - Weight is the force of gravity on an object. In physics, weight is measured in newtons. 

Work - Work occurs in physics when a force acts on an object to move it some distance. Work is equal to the force times the distance and is measured in joules.