Physics KS3/4: Gravity, size and mass

An organism’s structure, form and function are shaped by the process of evolution.

However, as Professor Cox explains, evolution is constrained by the universal forces of physics, like gravity.

He explains why gravity limits the size of plants and animals.

Using blocks of wood, he demonstrates how a doubling of linear size results in an eight-fold increase in mass.

He describes the limitations this relationship has on animals including the kangaroo and rhinoceros beetle.

This clip is from the series Wonders of Life.

Teacher Notes

Students can use an experiment to assess the effects of gravity.

Equipment needed is: a plastic cup, water, an outside area, a beaker or bucket.

Push a hole into the side of the cup. Cover with your thumb and fill with water.

Hold the cup up high and remove your thumb. The water will gush out easily.

Pose the question 'What would happen if you then dropped the cup?'

Repeat the experiment but drop it this time. You should observe the water not flowing out of the hole but remaining in the cup until it hits the floor. Gravity pulls down on the cup and water equally and does not push it through the hole.

Curriculum Notes

This clip will be relevant for teaching Physics and Biology. This topic appears in OCR, Edexcel, AQA, WJEC KS3, KS4 and GCSE in England and Wales, CCEA GCSE in Northern Ireland and SQA National 4/5 in Scotland.

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Conservation of energy
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How has life on Earth become so varied?
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Lemurs: Evolution and adaptation
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Jellyfish and photosynthesis
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The arrival of water on Earth
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The origins of life on Earth
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Evolution of hearing
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Evolution of sight
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Evolution of the senses
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Size and heat
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