What Are Gravitational Potential Energy and Kinetic Energy? | Physics in Motion

Summary

The video explains kinetic energy and gravitational potential energy, how to calculate them, and how they transform into one another.

Energy is the ability to do work. Under the law of conservation of energy, energy is not created or destroyed; it changes form.

Kinetic energy

Kinetic energy (KE) is the energy of motion. Examples include moving cars, sound waves, a rolling ball, and a walking person.

The formula is:

KE = ½mv²

where m is mass and v is velocity.

Kinetic energy is a scalar quantity, so it has no direction. The video also discusses energy being added to or taken away from a system; in that accounting, transfers can be treated as positive or negative.

For example, a 5.0 kg puppy moving at 2.2 m/s has 12.1 J of kinetic energy.

Potential energy

Potential energy (PE) is stored energy. The video mentions batteries, springs, and heat packs as examples of systems storing different forms of energy.

Gravitational potential energy (PE₍G₎) depends on an object’s mass and its height above a chosen reference point. Its formula is:

PE₍G₎ = mgh

Here, g is Earth’s gravitational acceleration (9.8 m/s²), and h is the height above the reference point. Choose a reference point—often the ground or the bottom of a ramp—and treat it as zero height.

For example, a 500.0 kg wrecking ball 12.2 m above the ground has about 59,780 J, or 5.98 × 10⁴ J, of gravitational potential energy.

Energy transformation

As an object descends, its gravitational potential energy decreases while its kinetic energy increases. A skateboarder, skier, or diver at a height has gravitational potential energy; as they fall or move downward, that energy converts into motion.

At the chosen reference point, the video describes gravitational potential energy as zero and kinetic energy as greatest.

Speakers and sources featured

• Unnamed presenter/narrator — explains the concepts and examples; also narrates the closing toolkit announcement.
• Sage — the puppy in the kinetic-energy example; not a speaking source.
• “Physics in Motion” toolkit — mentioned as a source of additional practice problems, lab activities, and note-taking guides.