Contrasting student and also scientific views

Student day-to-day experiences

Things falling towards the Earth are such familiar cases that students might take into consideration these occasions as ‘natural’ through no need for further explacountry.

You are watching: The gravitational force between two objects increases as mass

Even students who use the word ‘gravity’ in an proper context may not be able to have the ability to describe what it is, or will certainly be inconsistent in their explanations.

Research: Skamp (2004)

Students’ views around gravity, the shape of the Planet, and also the direction of ‘down’ are frequently linked.

This concept is also emerged in the focus concept Forces without contact.

Students may have actually a selection of views around gravity:

gravity is a press from above (in some instances because of air pressure)gravity is concerned the presence of air, or is something in the air, so if tright here is no air, tbelow is no gravity. (Hence tright here is no gravity on the moon, in Planet satellites or in space; as one rises above the surchallenge of the Planet gravity lessens because the setting thins)gravity boosts through heightgravity is considerably much less on high mountains or tall buildings and boosts as we lose height (which is why falling objects rate up)gravity is led to by the Planet spinninggravity affects points while they are falling yet stops once they reach the ground. It does not operate on points that are moving upwardsgravity acts upwards on things that are moving upwardsgravity is a huge forcethere is no gravity in a spacecraft orbiting the Planet.

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

Scientific view

Gravitational forces are thought about to be inherently connected to what we contact ‘mass’. Tbelow is a gravitational pressure of attraction between eincredibly object in the cosmos. The dimension of the gravitational force is proportional to the masses of the objects and weakens as the distance between them increases. Both objects exert an equal attrenergetic force on each other: a falling object is attracting the Earth through the exact same size pressure as the Planet is attracting it. The substantial distinction in mass between the Planet and also the falling object indicates the Earth’s motion is imperceptibly small.

We only notice gravitational pressures if one of the objects affiliated has actually a large mass (such as the Earth). In all attempts to compare gravitational pressures through various other forces, they are reasonably a lot weaker than magnetic and also electrical pressures.

Critical teaching ideas

Gravitational pressure is an attraction between masses.The higher the dimension of the masses, the higher the dimension of the gravitational pressure (also dubbed the gravity force).The gravitational pressure weakens swiftly via boosting distance between masses.The gravitational pressure is incredibly hard to detect unless at least among the objects has a lot of mass.Due to the fact that the Planet is so significant, you have to take a trip to an extremely great elevation over the Earth’s surchallenge prior to tbelow are any detectable alters in the gravitational pull of the Earth (there is only around 0.25% reduction at the top of Mt Everest).The weight force on an item tells us the size of the gravity force from Earth acting on the object.

Explore the relationships between concepts around gravity in the Concept Growth Map - (Gravity, Stars)

It is advantageous to emphasis individually on two locations where gravity is important:

1. Near the Earth’s surface

Students need avenues for discussion that draws out the idea that gravity pressures on objects are exerted by the whole Earth towards its centre. A gravity force acts on an item regardmuch less of whether it is relocating or not relocating. In everyday situations, the dimension of the gravity pressure on something does not readjust significantly as it rises over the Planet. (An object demands to go a lot higher than a jumbo jet for significant distinctions to take place. The dimension of the gravity force at an altitude of 200km is still around 94% of what it was at sea level.)

The gravity pressure on an object from the Planet is the same regardless of whether the object is surrounded by air (or water or anypoint else).

Research: Mitchell (2007)

2. The universe

It is advantageous if students understand that the Earth and also various other planets orlittle bit the sun, and also that as soon as things adjust direction (as the planets are constantly doing) they have a pressure on them.

This principle is likewise arisen in the focus ideas Pushes and also pulls; What is a force? and also Day and night.

The idea that there should be a pressure on the planets that changes their direction deserve to be connected to the gravity pressure of the Earth on objects near its surface, therefore helping students to understand also the generalisation that gravity pressures exist almost everywhere in the universe.

Film or videotapes demonstrating the gravitational forces in between objects, and that astronauts were able to walk on the moon and also drop objects on it because of the moon’s gravity, deserve to assist make these concepts plausible for students.

Teaching activities

Challenge some existing ideas

POE (Predict-Observe-Explain): a spring balance via a weight attached hangs inside a sealed bell jar linked to a vacuum pump. Ask students to predict whether, and also how, the spring balance analysis will change when the air is pumped out. Then ask them to explain their observations. Note: It is advantageous to present beforehand also that the analysis registers a reduction in a net downward pressure if the weight is inserted in water as a result of the upward push of water. See the diagrams.


Bring out students’ existing ideas

Get students to think about whether the gravity pressure on them currently is a lot more/a little bit more/the same/a lot less/a tiny little less/zero once they are:

in the exact same classroom with all the air pumped outon optimal of Mt Evereston peak of the tallest structure in Melbourneon the moon (1/6 the size of Earth)in the classroom however the Planet has quit spinningbeside an additional astronaut in deep spacethe just astronaut in deep spacein totally free autumn after jumping from a aircraft.

Collate responses and conduct a entirety class interpretive conversation to clarify students’ thinking and indevelop even more teaching.

Research: Gunrock & Mitche​ll (1998)

Promote reflection on and also clarification of existing ideas

Encourage classroom discussions (interpretive discussions) which check out the interactivity of gravity forces via air resistance and frictional pressures. An approach is to compare the movement of 2 sheets of paper, one flat and the other crumpled right into a tiny round, once they are released at the very same time from the same height. The gravitational pressures acting on each are the very same but their loved one motion is extremely different as a result of the activity of air resistance. Extfinish the discussion to discover the pressures acting on skydivers in the time of cost-free autumn and once making use of parachutes.

POE (Predict-Observe-Explain): to help students think around their family member sizes, ask students to predict which of these forces is smallest: magnetic, electric or gravity forces. Then ask them to observe a hair sticking to a charged comb and a hair clip sticking to a magnet. In the occurring discussion, it may be helpful to allude out that the entirety of the Earth is pulling on the hair/hair clip. While this task is imspecific it opens up up discussions about the relative strengths of these pressures.

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Assistance students to work-related out some of the ‘scientific’ explanation for themselves

Using the internet, students have the right to look for examples of ‘weightlessness’ and build explanations utilizing concepts around universal gravitation.