Glossary
Conservation of Energy
A fundamental principle stating that energy cannot be created or destroyed, only transformed from one form to another or transferred between objects within a closed system. The total energy of a closed system remains constant.
Example:
When a roller coaster goes down a hill, its gravitational potential energy is converted into kinetic energy, but the total mechanical energy (ignoring friction) remains constant due to the principle of conservation of energy.
Conservation of Energy
A fundamental principle stating that energy cannot be created or destroyed, only transformed from one form to another. In isolated systems, the total mechanical energy (kinetic + potential) remains constant.
Example:
As a roller coaster descends a hill, its potential energy is converted into kinetic energy, demonstrating the conservation of energy.
Direction
The path or orientation along which a vector quantity acts. Unlike velocity, kinetic energy does not have a direction.
Example:
When a rocket launches, its velocity has both a direction (upwards) and a magnitude (speed).
Frame of Reference
A coordinate system or point from which observations of motion are made. An object's kinetic energy can appear different depending on the observer's frame of reference.
Example:
To someone standing on the ground, a person walking on a moving train has a certain speed, but to someone sitting on the train, that person's speed relative to their frame of reference might be much slower.
Frame-dependent
A property of a physical quantity whose value depends on the observer's reference frame. Kinetic energy is frame-dependent.
Example:
Your kinetic energy is zero relative to your seat on a moving train, but it is non-zero and frame-dependent when observed from the ground.
Inertial Reference Frame
A non-accelerating reference frame where Newton's laws of motion hold true. The ground is often considered a convenient inertial reference frame for many physics problems.
Example:
When analyzing the motion of a projectile, we typically use the Earth's surface as an inertial reference frame.
Joule (J)
The SI unit of energy, including kinetic energy. One joule is defined as the work done by a force of one newton moving an object one meter.
Example:
A small apple falling from a height of one meter gains approximately 1 Joule of kinetic energy just before hitting the ground.
Joules (J)
The standard SI unit of energy, including kinetic energy, and work. One Joule is equivalent to one Newton-meter (N·m) or one kilogram-meter squared per second squared (kg·m²/s²).
Example:
Lifting a 1 kg apple approximately 1 meter off the ground requires about 10 Joules of energy.
Kilogram (kg)
The SI unit of mass. It is a fundamental unit used in the calculation of kinetic energy.
Example:
A standard physics lab uses masses measured in kilograms, such as a 2 kg block on an air track.
Kinetic Energy
The energy an object possesses due to its motion. It is a scalar quantity, always positive or zero, and depends on both the object's mass and speed.
Example:
A baseball thrown at high speed has significant kinetic energy, which allows it to break a window upon impact.
Kinetic Energy (KE)
The energy an object possesses due to its motion. It is a scalar quantity that depends on an object's mass and speed.
Example:
A baseball thrown by a pitcher has significant kinetic energy as it flies towards home plate, allowing it to break a pane of glass upon impact.
Magnitude
The size or amount of a physical quantity. For scalar quantities like kinetic energy, magnitude is the sole descriptor.
Example:
The magnitude of a car's velocity might be 60 mph, regardless of whether it's heading north or south.
Mass
A measure of the amount of matter in an object, typically measured in kilograms. It is a direct factor in determining an object's kinetic energy.
Example:
A bowling ball has a much larger mass than a tennis ball, which contributes to its greater kinetic energy when moving at the same speed.
Mass (m)
A fundamental property of matter that quantifies its inertia, or resistance to changes in motion. In the kinetic energy formula, it is measured in kilograms (kg).
Example:
A bowling ball has a much larger mass than a tennis ball, which is why it's harder to get it moving and stop it once it is in motion.
Meter per second (m/s)
The SI unit of speed or velocity. Velocity is squared in the kinetic energy formula, making it a dominant factor.
Example:
A sprinter running at 10 meter per second has a significant amount of kinetic energy due to their speed.
Momentum
A vector quantity defined as the product of an object's mass and its velocity (p = mv). While distinct from kinetic energy, it is often conserved in collisions and interactions.
Example:
A heavy truck moving slowly can have the same momentum as a light car moving quickly.
Potential Energy
Stored energy an object possesses due to its position or configuration. In mechanics, this often refers to gravitational potential energy (mgh) or elastic potential energy (½kx²).
Example:
A book held high above the ground has gravitational potential energy that can be converted into kinetic energy if it falls.
Scalar Quantity
A physical quantity that has magnitude (size) only and no direction. Kinetic energy is an example of a scalar quantity.
Example:
If you measure the temperature of a room, you only state its value (e.g., 20°C) without a direction, making temperature a scalar quantity.
Scalar quantity
A physical quantity that has magnitude but no direction. Kinetic energy is a scalar, meaning it is always positive or zero.
Example:
Temperature is a scalar quantity; it tells you how hot or cold something is, but not in what direction.
Translational Kinetic Energy
The specific type of kinetic energy associated with an object's linear motion, as opposed to rotational motion. It quantifies the 'oomph' an object has from moving from one place to another.
Example:
When a car drives down a straight road, its forward movement is an example of translational kinetic energy.
Translational Kinetic Energy
The specific type of kinetic energy associated with an object's linear motion from one point to another. It is calculated using the formula K = ½mv².
Example:
When a car drives down a straight road, its movement represents translational kinetic energy.
Velocity
A vector quantity describing an object's speed and direction of motion. In the kinetic energy formula, its magnitude (speed) is squared.
Example:
A car's velocity might be 30 m/s East, indicating both its speed and its direction of travel.
Velocity (v)
A vector quantity that describes both the speed and direction of an object's motion. In the kinetic energy formula, only its magnitude (speed) is used, and it is measured in meters per second (m/s).
Example:
A rocket launching upwards at 100 m/s has a specific velocity, indicating both its speed and its upward direction.
Work-Energy Theorem
States that the net work done on an object is equal to the change in its kinetic energy. This theorem provides a direct link between work and energy.
Example:
If you push a box across the floor, the work-energy theorem tells you that the work you do on the box will increase its kinetic energy, making it speed up.
Work-Energy Theorem
States that the net work done on an object is equal to the change in its kinetic energy. This theorem provides a powerful link between force, displacement, and energy.
Example:
If a constant force does 10 J of work on a stationary object, the Work-Energy Theorem tells us the object will gain 10 J of kinetic energy.