Energy in Motion Study Guide

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Main Concepts:

Similarly, when an object has maximum potential energy, it can still have kinetic energy but the kinetic energy would be at its minimum. An object can still have speed even when it is at its highest location in space.

For Newton’s laws, the most common misconception is that mass and weight are the same. However, mass is the amount of matter in an object and always remains the same regardless of location(i.e. it would have the same mass and gravity does not have an impact on it). Weight is the effect of gravity on mass and it depends on location.

Another main concept in this unit is the relationship between energy and force. If a force results in motion, it has performed work, meaning that energy was expended. Thus, energy and forces are related through the transfer and transformation of one type of energy to another through forces and work.


Maximum Potential Energy- stored energy; an object can still be moving while having maximum potential energy. The maximum potential energy is always at the highest position of an object’s trajectory and the slowest point of an object’s travel.

Kinetic Energy(KE)- energy due to motion; formula: KE = 1/2 * mv² where m is the mass of the object and v is the velocity/ speed of the object. A change in an object’s motion depends on the forces acting on the objects and its mass.

Maximum Kinetic Energy- energy of motion; Always at the spot of initial force(throw/arc); lowest point in an object’s trajectory, fastest point in an object’s travel

Total Energy- the sum of all the types of energies in an object; Total Energy does not transfer and always remains the same

Mechanical Energy- the sum of the kinetic energy and potential energy; Mechanical energy of an object remains the same unless it transfers some of it to another object; Even if mechanical energy is constant, KE and PE can still increase and decrease

Magnitude- size

Energy transformation- change from one form of energy to another; any form of energy can change into any other form of energy.

System-Open- an open system where matter and energy can go in and out

System-Closed- a closed system where matter and energy cannot go in or out

Model-representation of something

Friction- a contact force; a type of thermal energy created from the sliding motion of two surfaces; amount of friction depends on the materials that are touching; friction can also act on objects moving through air/water; coefficient of friction shows amount of friction between two surfaces. Larger coefficient of friction means greater friction; friction ALWAYS creates heat

Law of Conservation of Energy: Energy is never created nor destroyed, but is transferred and transformed in a system. The total amount of energy in a closed system always adds up to the same amount of total energy. Energy can change from one form to another but always adds up to the same amount of total energy.

Force- a push or pull exerted by an object.Force is a vector quantity(has magnitude and direction) measured in Newtons(N) and is needed to overcome inertia; Balanced forces acting on an object do not cause a change in motion because they cancel out. The motion of an object will only change when unbalanced forces act on an object. Contact force is when two objects are touching when a force is exerted. Field force is a force exerted over a distance without objects touching.

Acceleration- a change in velocity(speed and direction); Unit: m/s²

Types of Variables:

Dependent Variable: the one thing in an experiment that is being measured and the variable that changes due to the independent variable

Control: the variables that stay the same in order to observe the relationship between the independent and dependent variables

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Types of Energy

Chemical energy is the energy of a compound and changes when the atoms are rearranged. It is a type of potential energy because it is dependent on the position and arrangement of atoms.

Electrical energy is the energy of moving electrons. Generators turn magnets inside loops of wire and its changing position makes electricity run through the wires. Electrical energy is stored as potential energy before use.

Sound energy is caused by electrical vibrations. For example, when a guitar string is stretched, it has potential energy in it because it experiences a change in shape due to work. When the string is released, it vibrates with kinetic energy. Some of the kinetic energy is transmitted into the air, creating air vibrations, thus creating sound.

Light energy is produced by the vibrations of electrically charged particles. Both light energy and sound energy are caused by vibrations. Unlike sound energy however, light energy does not require a medium to travel through, meaning that light can travel through a vacuum(area of no matter).

How are Energies and Forces related?

Newton’s Laws of Motion

Newton’s Cradle(representation of Newton’s first law of motion) Image Source

Inertia- an object’s tendency to resist any change in motion

Newton’s Second Law of Motion- F = ma, Force equals mass times acceleration

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Newton’s Third Law of Motion- For every force, there is an equal and opposite reaction.


G is the gravitational constant, (6.67 * 10^-11), r is the distance between the two masses, the m’s are the masses of the objects while Fg is the gravitational force. The gravitational force is equal to the gravitational constant times the masses of the two objects, divided by their distance squared. Image Source

Mass and Weight

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Credit to: Houghton Mifflin Harcourt Publishing Company, Physical Science, Core Skills Science, Grade 8 articles



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