Space Physics: gravity force, weight, difference on other planets, between earth and moon and earth and sun
Gravity is a difficult topic to find practical activities for, but here are a few suggestions for demonstrations and experiments.
Visit the practical work page to access all resources and lists focussing on practical work in secondary science: www.nationalstemcentre.org.uk/sciencepracticals
Earth in Space 11-14
Gravity is a topic full of misconceptions and teachers who lack confidence in this topic will greatly appreciate the structure offered by this resource from the Institute of Physics and will want to take the opportunity to read around the subject a little.
Here we focus on two activities from ES01: 1 Beam Hanging and 3 Tins of Beans. Once you have down loaded the file choose the ES01 TA document. Background notes can be found in ES01 PN and ES01 PL.
Beam Hanging is an excellent introduction to the idea of gravity and would make a super lesson starter. It will challenge students to think through exactly what they mean when they talk about gravity.
Follow this up with the Tins of Beans activity where students experience the weight of tins on different planets. This practical work will help make clear the difference between mass and weight. There is the opportunity to introduce students to simple and more complex calculations and think about the units used. Note that the activity uses 200g tins of beans. If teachers want to use the more standard 415g size then the weights will need scaling up appropriately.
The Earth's gravitational pull
Students readily gain a simple understanding of gravity; this piece of practical work is designed to help them think more deeply about how gravity acts. The experiment is simple to perform so students won’t need written instructions.
By imagining gravity as the force from a spring connecting an object to the ground, students examine what happens to the force when the imaginary spring is stretched, ie the object is lifted higher. It is recommended that several sets of equipment are made available so that all students in the class can check the measurements for themselves.
The teacher guidance at the bottom of the page explains why the model is still a good one, even though no change can be detected and goes on to give the example of spacecraft where the force from gravity is significantly smaller.
Circular motion
It’s gravity that keeps the Moon in orbit around the Earth and the Earth in orbit around the Sun. The Moon is pulled in towards the Earth and that’s what keeps it travelling in a circle. If gravity suddenly disappeared, the Moon would keep travelling in a straight line in whatever direction it was heading at the time – remember a force is needed to change the direction of an object.
This is a difficult concept for students and so demonstrations like this one are helpful to get students thinking about circular motion. Ask them what the bung might represent and what the string represents.
You could follow this demonstration up with the “whirling a bung and letting go” which is hyperlinked at the bottom of the page.