## Contrasting student and also scientific views

### Student everyday experiences

Things falling in the direction of the planet are such acquainted occurrences the students may take into consideration these events as ‘natural’ through no require for more explanation.

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Even students that use words ‘gravity’ in an proper context might not have the ability to be able to explain what the is, or will certainly be inconsistent in their explanations.

Research: Skamp (2004)

Students’ views around gravity, the shape of the Earth, and the direction the ‘down’ are frequently intertwined.

This idea is also developed in the emphasis idea forces without contact.

Students may have a variety of views around gravity:

gravity is a push from over (in some instances because of air pressure)gravity is regarded the visibility of air, or is miscellaneous in the air, so if there is no air, over there is no gravity. (Hence there is no gravity on the moon, in earth satellites or in space; as one rises over the surface ar of the planet gravity lessens since the atmosphere thins)gravity increases with heightgravity is significantly less top top high hills or tall buildings and increases as we lose elevation (which is why falling objects rate up)gravity is brought about by the planet spinninggravity affects things while they room falling however stops when they with the ground. The does not run on points that are relocating upwardsgravity action upwards on points that are moving upwardsgravity is a huge forcethere is no heaviness in a spacecraft orbiting the Earth.

Research: Skamp (2004), Palmer (2001), Gunstone & Mitchell (1998), Gunstone & watt (1985), watt (1982)

### Scientific view

Gravitational pressures are taken into consideration to it is in inherently linked to what we call ‘mass’. Over there is a gravitational pressure of attraction in between every object in the universe. The dimension of the gravitational force is proportional come the masses the the objects and also weakens together the distance in between them increases. Both objects exert an same attractive pressure on each other: a falling thing is attracting the earth with the very same size pressure as the planet is attracting it. The huge difference in mass in between the Earth and the falling object method the Earth’s activity is imperceptibly small.

We only an alert gravitational forces if among the objects involved has a vast mass (such as the Earth). In all attempts to to compare gravitational pressures with various other forces, lock are relatively much weaker than magnetic and also electric forces.

## Critical teaching ideas

Gravitational pressure is one attraction in between masses.The better the size of the masses, the higher the size of the gravitational force (also referred to as the gravity force).The gravitational force weakens swiftly with enhancing distance between masses.The gravitational pressure is very hard to detect unless at least one of the objects has actually a many mass.Because the planet is for this reason big, you have to travel to a very good height above the earth’s surface prior to there are any type of detectable alters in the gravitational traction of the earth (there is only about 0.25% palliation at the height of Mt Everest).The weight force on an object tells united state the dimension of the gravity force from earth acting ~ above the object.

Explore the relationships in between ideas about gravity in the Concept breakthrough Map - (Gravity, Stars)

It is valuable to focus separately ~ above two locations where gravity is important:

### 1. Close to the earth’s surface

Students need opportunities for conversation that draws out the idea that gravity forces on objects room exerted by the whole planet towards that centre. A gravity force acts on an object regardless of even if it is it is relocating or no moving. In daily situations, the dimension of the gravity force on something walk not readjust significantly as it rises over the Earth. (An object demands to walk much higher than a jumbo jet for significant differences to occur. The size of the gravity force at one altitude of 200km is still around 94% of what it was at sea level.)

The gravity pressure on an item from the planet is the exact same regardless of whether the thing is surrounding by waiting (or water or something else).

Research: Mitchell (2007)

### 2. The universe

It is helpful if students know that the Earth and other planets orbit the sun, and that as soon as things adjust direction (as the planets space constantly doing) they have actually a force on them.

This idea is also developed in the focus ideas Pushes and also pulls; What is a force? and Day and night.

The idea the there should be a force on the planets that alters their direction deserve to be connected to the gravity force of the planet on objects near its surface, for this reason helping student to recognize the generalisation that gravity forces exist everywhere in the universe.

Film or videotapes demonstrating the gravitational forces in between objects, and also that astronauts were able to walk ~ above the moon and drop objects top top it due to the fact that of the moon’s gravity, can help make these principles plausible for students.

## Teaching activities

### Challenge part existing ideas

POE (Predict-Observe-Explain): a spring balance with a load attached hangs within a sealed bell jar linked to a vacuum pump. Ask students come predict whether, and also how, the feather balance reading will change when the air is pumped out. Climate ask lock to describe their observations. Note: that is advantageous to display beforehand the the reading registers a palliation in a net downward pressure if the load is inserted in water due to the upward push of water. See the diagrams.

### Bring out students’ currently ideas

Get students come think about whether the gravity force on them now is a lot more/a little more/the same/a many less/a tiny little less/zero as soon as they are:

in the exact same classroom v all the air pumped outon top of Mt Evereston top of the tallest structure in Melbourneon the moon (1/6 the size of Earth)in the classroom but the planet has quit spinningnext to one more astronaut in deep spacethe just astronaut in deep spacein totally free fall after ~ jumping native a plane.

Collate responses and also conduct a whole course interpretive discussion to clarify students’ thinking and also inform further teaching.

Research: Gunstone & Mitche​ll (1998)

### Promote reflection on and also clarification of currently ideas

Encourage class discussions (interpretive discussions) which check out the communication of gravity pressures with waiting resistance and also frictional forces. An approach is to to compare the movement of two sheets that paper, one flat and the various other crumpled right into a small ball, once they space released in ~ the very same time native the exact same height. The gravitational forces acting ~ above each room the same but their relative motion is an extremely different as result of the activity of wait resistance. Expand the conversation to discover the forces acting top top skydivers during totally free fall and also when making use of parachutes.

POE (Predict-Observe-Explain): to help students think around their relative sizes, ask students come predict i beg your pardon of these forces is smallest: magnetic, electric or heaviness forces. Climate ask castle to observe a hair sticking to a charged comb and also a hair clip sticking to a magnet. In the ensuing discussion, it might be beneficial to point out the the whole of the earth is pulling top top the hair/hair clip. When this task is imprecise it opens up discussions around the family member strengths of these forces.

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### Help student to occupational out few of the ‘scientific’ explanation because that themselves

Using the internet, students deserve to look for examples of ‘weightlessness’ and develop explanations utilizing ideas about universal gravitation.