Gravitational potential energy (Ep = m g h)

What you need to know

• Raising an object increases its gravitational potential energy — energy is transferred into the gravitational store.
• Use Ep = m g h where g ≈ 9.8 N/kg near Earth's surface.
• h is the change in vertical height in metres — not the distance along a slope or path.
• When an object falls, gravitational potential energy transfers to the kinetic energy store.

The big picture

When an object is raised in a gravitational field, energy is transferred into its gravitational potential store. The higher the object, the greater the mass, and the stronger the gravitational field, the more energy is stored. This is calculated using Ep = m g h. When the object falls, that stored energy converts into kinetic energy — the core of almost every energy-transfer problem you'll meet at GCSE.

How gravitational potential energy builds and releases

Follow one object through the process — from being lifted to falling.

1. 1

   Object is lifted upward

   A force acts on the object over a vertical distance. Work is done against gravity, so energy is transferred from whatever is doing the lifting into the object's gravitational potential store.

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2. 2

   Object sits at height h

   The object now has gravitational potential energy equal to Ep = m g h. This energy is stored — not released yet. It depends on mass, gravitational field strength, and the vertical height above the reference point.

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3. 3

   Object begins to fall

   As the object descends, height h decreases. The gravitational potential energy store empties — energy is transferred into the kinetic energy store. The object speeds up.

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4. 4

   Object reaches the ground

   At the original reference height, h = 0, so Ep = 0. All the original gravitational potential energy has been transferred — into kinetic energy (and some thermal energy if friction acted). The energy stores have changed but the total energy is conserved.

Stop and predict

Commit to an answer before you reveal — this is where the learning happens.

A 2 kg book is placed on a shelf 1 m high. A 4 kg book is placed on a shelf 0.5 m high. Using g = 9.8 N/kg — which book has MORE gravitational potential energy stored?

Tap any cell to reveal it. Tap a column header to read one property down every item.

Taken directly from the exam-board specification.

Memory hook

Think 'MGH' as 'My Great Height' — Mass × g × Height gives the energy stored at that height.

Check yourself

Without looking — which three quantities do you multiply together to find gravitational potential energy, and what are their units?