Forces Motion And Energy: Science Terms Explained
Plain-language definitions of every forces motion and energy term your child meets in school, each with kid-friendly explanations, worked examples, and common mistakes to watch for.
Acceleration
Acceleration is the rate at which an object's velocity changes, which means how quickly it speeds up, slows down, or changes direction over time.
Amplitude of a wave
Amplitude of a wave is the maximum distance a point on the wave moves away from its rest position, showing how strong or intense the wave is.
Balanced and unbalanced forces
Balanced and unbalanced forces describe how pushes and pulls on an object combine: balanced forces cancel each other so motion does not change, while unbalanced forces do not cancel and cause the object to start moving, stop, or change direction.
Chemical energy
Chemical energy is energy stored in the bonds between atoms in a substance, which can be released or absorbed during a chemical reaction when those bonds are broken or rearranged.
Conduction
Conduction is the transfer of thermal energy (heat) between particles that are touching, usually in a solid, as faster-moving particles bump into slower ones and pass their energy along.
Conservation of energy
Conservation of energy is the scientific idea that energy cannot be created or destroyed, only changed from one form to another or transferred from one place to another, so the total amount of energy in a closed system stays the same.
Convection
Convection is the transfer of thermal energy by the movement of a fluid, such as a liquid or gas, when warmer, less dense regions rise and cooler, denser regions sink, creating a circulating flow of material and heat.
Electromagnetic spectrum
The electromagnetic spectrum is the full range of all types of electromagnetic waves, from low-energy radio waves to high-energy gamma rays, arranged by their wavelength or frequency.
Energy
Energy is the ability to do work or cause change, such as moving objects, heating things up, making light, or powering devices.
Energy transfer
Energy transfer is the movement of energy from one object or place to another, such as when moving objects collide or when heat flows from something warm to something cooler.
Energy transformation
Energy transformation is the process of energy changing from one form, such as light or motion, into another form, such as heat or sound, while the total amount of energy stays the same.
Frequency
Frequency is the number of times something repeats in a certain amount of time, such as how many wave cycles, vibrations, or swings happen each second.
Friction
Friction is a force that happens when two surfaces touch and rub against each other, slowing or stopping motion and often turning some of the motion energy into heat.
Gravity
Gravity is the force of attraction that pulls objects with mass toward each other, such as pulling you, your chair, and the air around you toward Earth.
Heat
Heat is the transfer of thermal energy from a hotter object to a colder one because of a temperature difference, and it continues to flow until both are the same temperature.
Inclined plane
An inclined plane is a flat surface that is tilted, or slanted, so one end is higher than the other, which lets you move objects up or down with less force than lifting them straight up.
Inertia
Inertia is an object's tendency to keep doing what it is already doing, staying at rest or moving in a straight line at the same speed, unless a force acts on it.
Kinetic energy
Kinetic energy is the energy an object has because it is moving, and it increases when the object moves faster or has more mass.
Lever
A lever is a simple machine made of a stiff bar that turns around a fixed point, called a fulcrum, to help lift or move a load with less effort.
Light
Light is a form of energy that travels in waves and lets us see, moving very quickly through space and many materials, but not through everything.
Mass and weight
Mass and weight are related but different: mass is how much matter is in an object, and weight is the force of gravity pulling on that mass.
Mechanical energy
Mechanical energy is the total energy an object has because of its motion and its position, which is found by adding its kinetic energy (energy of motion) and potential energy (stored energy due to position).
Momentum
Momentum is the quantity of motion an object has, calculated by multiplying its mass by its velocity, and it describes how hard it is to stop or change that object's motion.
Motion
Motion is a change in an object's position over time compared with something else, which shows that the object is moving rather than staying still.
Newton's first law
Newton's first law is the rule that an object will stay at rest or keep moving in a straight line at a constant speed unless a net (unbalanced) force acts on it.
Newton's laws of motion
Newton's laws of motion are three basic rules that describe how forces affect the motion of objects, explaining why objects stay still, speed up, slow down, or change direction.
Newton's second law
Newton's second law is the idea that the acceleration of an object depends on the net force acting on it and its mass, usually written as F = m × a, where F is net force, m is mass, and a is acceleration.
Newton's third law
Newton's third law is the idea that whenever one object pushes or pulls on another object, the second object pushes or pulls back with an equal-strength force in the opposite direction.
Pitch
Pitch is how high or low a sound seems to your ears, which is mainly determined by how fast the sound waves are vibrating (their frequency).
Potential energy
Potential energy is stored energy that an object has because of its position or condition, which can be changed into motion or other forms of energy later.
Pulley
A pulley is a simple machine made of a wheel with a groove around its edge and a rope, cable, or chain that runs through the groove, used to lift or move loads by changing the direction or size of a force.
Radiation
Radiation is the transfer of energy through waves or particles that can travel through empty space, such as the energy we receive from the Sun as light and heat.
Reflection of light
Reflection of light is when light rays hit a surface and bounce back, changing direction instead of passing through or being absorbed.
Refraction
Refraction is the bending of a wave, such as light, as it passes from one material into another where it travels at a different speed.
Screw
A screw is a simple machine made of a metal rod with a slanted groove wrapped around it, which lets you turn a small twisting force into a stronger force that can hold things together or lift objects.
Simple machines
Simple machines are basic devices with few or no moving parts that change the size or direction of a force to make work easier, such as levers, ramps, and pulleys.
Sound wave
A sound wave is a pattern of vibrations that travels through a material, such as air, water, or a solid, carrying sound from one place to another.
Speed
Speed is how fast something moves, measured by how much distance it travels in a certain amount of time, such as meters per second or miles per hour.
Speed of light
The speed of light is the constant speed at which light and all other electromagnetic waves travel in a vacuum, equal to about 3.0 × 108 meters per second (approximately 300,000 kilometers per second).
Temperature and heat
Temperature and heat are related ideas in science: temperature measures how hot or cold something is, while heat is the energy that moves from a warmer object to a cooler one because of their temperature difference.
Thermal energy
Thermal energy is the total kinetic energy of all the tiny moving particles in a substance, which we sense as how hot or cold something is.
Velocity
Velocity is the speed of an object in a specific direction, such as 10 meters per second north.
Vibration
Vibration is a back-and-forth or up-and-down motion that repeats over and over around a central position, often caused when an object is disturbed and energy moves through it.
Visible light
Visible light is the range of electromagnetic energy that human eyes can detect, made up of different colors from red to violet that together let us see the world.
Wave
A wave is a repeating disturbance that transfers energy from one place to another without moving matter from place to place in the same way.
Wavelength
A wavelength is the distance between two matching points on a wave, such as from one crest (highest point) to the next crest, and it shows how long one full wave is in space.
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