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Observations and Conclusions

From the experiment we find that the slope of the graph (weight in N against mass in kg) is a straight line going through the origin, so :

weight α mass

therefore

weight = constant x mass

The value which remains constant, in this experiment, is the pull of the Earth's gravity, and so:

 weight = mass x gravity W = m g In this equation, weight is measured in N, mass in kg gravity in Nkg -1.

Weight is dependant on gravity and so by using the above equation you can convert a mass into a weight and vice versa. As a consequence, if the gravity is zero the weight is zero:

W = m x 0

So an object in space is weightless.

We also find that the weight of a 1 kg mass is 9.81 N.

We usually use 10N to make calculations easier : this means that 1N is the weight of an average sized apple!

Gravity and therefore weight, varies slightly depending on where you are on the Earth:

In Paris and London : g = 9.81 Nkg -1

PHYSICAL SCIENCE

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Mechanics

To find the relationship between mass and weight

Apparatus

Various objects or masses (between 5 and 8), balance, newton-meters (1N and 5N)

Method

• Find the mass of an object using the balance.

• Find its corresponding weight using a newton-meter (start with the least sensitive-5N -first) but if its weight is under 1N, use the 1N newton-meter.

• Repeat this procedure using the other objects.

• Draw a graph of weight in N against mass in kg.

• Calculate the slope of this graph.

Results

 Object Weight in newtons (N) Mass in grams (g) Mass in kg

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