The energy of objects in a gravitational field (dGPE=m x g x dh)
Lesson details
Learning outcome
I can calculate the change in energy of an object because of its movement in a gravitational field.
Key learning points
- When an object moves upwards, work is done against the gravitational force.
- The gravitational force acting on an object does work to speed it up when it is falling.
- Weight = mass x gravitational field strength, W = mg
- Change in gravitational potential energy of an object = mass × gravitational field strength × change in height
Keywords
Gravitational store - Objects have energy in the gravitational store because of their mass and their height.
Work done - Work is done whenever a force makes an object move. The amount of work done is equal to the force multiplied by distance moved in the direction of the force.
Weight - Weight = mass × gravitational field strength, measured in newtons.
Gravitational field strength - Gravitational field strength, g, is the force per kilogram caused by a gravitational field.
Gravitational potential energy - The energy stored in an object due to its height above the ground.
Common misconception
Pupils often think that the amount of energy in the gravitational store depends on the path taken by an object to change its height, or the speed of an object at a particular height.
Teaching should include examples of objects increasing height by the same amount by different routes, and examples of objects at the same height moving at different speeds.
Teacher tip
If it is appropriate for your class, this is a good lesson for giving pupils calculations that include values written in standard form.
Licence
except where otherwise stated. See Oak's terms & conditions (Collection 2).Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Which properties of an object can be increased so it has more energy in its gravitational store?
Q2.Why does an object that is dropped accelerate downwards?
Q3.What happens to the amount of work done lifting a box of books, if the box is lifted to four times the height?
Q4.In science, what unit is the weight of an object measured in?
Q5.How would you calculate the work done lifting a sack of onions onto a table?
Q6.The gravitational force on Earth is six times greater than it is on the Moon. Put the following tools in order of the amount of energy in the gravitational store, starting with the most energy.
Assessment exit quiz
6 Questions
Q1.How much energy will be transferred to the gravitational store if two times the amount of work is done lifting a tray of cakes?
Q2.Which of these identical basketballs has the most energy in the gravitational store?
Q3.What happens to the amount of energy in the gravitational store of a pile of bricks on a table if more bricks are added to double its mass?
Q4.What is gravitational potential energy?
Q5.What is the gravitational energy of a discus of mass 2 kg moving at a speed of 8 m/s that is 9 m above the ground? (Gravitational field strength = 10 N/kg)
Q6.What is the height of a javelin that has a gravitational energy of 216 J, a mass of 1.2 kg, and a speed of 12 m/s? (Gravitational field strength = 10 N/kg)
To help you plan your 10 physics lesson on: The energy of objects in a gravitational field (dGPE=m x g x dh), download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 10 physics lesson on: The energy of objects in a gravitational field (dGPE=m x g x dh), download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
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The assessment exit quiz will test your pupils' understanding of the key learning points.
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Explore more key stage 4 physics lessons from the Energy of moving objects unit, dive into the full secondary physics curriculum, or learn more about lesson planning.