Introduction to forces

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(New page: ==Newton's First Law== A particle will move with a constant velocity or remain at rest if the resultant force on the particle is zero. '''Equilibrium''' If the resultant force on a par...)
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<math>\text{5}.\text{98}\times \text{1}0^{\text{24}}\text{ }</math>
<math>\text{5}.\text{98}\times \text{1}0^{\text{24}}\text{ }</math>
kg
kg
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'''[[Example 2.1]]'''
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Describe whether or not the forces acting on the following objects are in equilibrium:
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(a) A passenger in a train that travels at a constant speed.
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(b) A hot air balloon rising at a constant rate.
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(c) A stone dropped into a very deep well full of water.
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'''Solution'''
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(a) Yes, if it is travelling in a straight line.
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(b) Yes, if it is travelling in a straight line.
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(c) Yes, if it reaches a terminal velocity, so that it is travelling in a straight line at a constant speed.
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'''[[Example 2.2]]'''
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Find the magnitude of the force of gravity (weight) acting on a lorry of mass 22 tonnes.
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'''Solution'''
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This is calculated using the fact that the weight is given by mg.
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<math>\begin{align}
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& mg=22000\times 9.8 \\
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& =215600\text{ N}
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\end{align}</math>
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The diagram shows the lorry and its weight.
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Note that reaction forces also act upwards on each wheel.
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<math>R_{1}+R_{2}+R_{3}+R_{4}=215600</math>

Revision as of 14:59, 13 March 2009

Newton's First Law

A particle will move with a constant velocity or remain at rest if the resultant force on the particle is zero.

Equilibrium

If the resultant force on a particle is zero, then the forces acting on the particle are said to be in equilibrium.

The Universal Law of Gravitation


\displaystyle F=\frac{Gm_{1}m_{2}}{d^{2}}


\displaystyle G=6.67\times 10^{-11}\text{ kg}^{\text{-1}}\text{m}^{\text{3}}\text{s}^{\text{-2}}


Gravity on Earth

The force of gravity is often called the weight.


\displaystyle \begin{align} & F=mg \\ & g=9.8\text{ ms}^{\text{-2}} \\ \end{align}


Data


Radius of Earth is \displaystyle \text{6}.\text{37}\times \text{1}0^{\text{6}}\text{ } metres

Mass of Earth is \displaystyle \text{5}.\text{98}\times \text{1}0^{\text{24}}\text{ } kg


Example 2.1

Describe whether or not the forces acting on the following objects are in equilibrium:

(a) A passenger in a train that travels at a constant speed.

(b) A hot air balloon rising at a constant rate.

(c) A stone dropped into a very deep well full of water.

Solution

(a) Yes, if it is travelling in a straight line.

(b) Yes, if it is travelling in a straight line.

(c) Yes, if it reaches a terminal velocity, so that it is travelling in a straight line at a constant speed.


Example 2.2

Find the magnitude of the force of gravity (weight) acting on a lorry of mass 22 tonnes.

Solution

This is calculated using the fact that the weight is given by mg.


\displaystyle \begin{align} & mg=22000\times 9.8 \\ & =215600\text{ N} \end{align}


The diagram shows the lorry and its weight.


Note that reaction forces also act upwards on each wheel.


\displaystyle R_{1}+R_{2}+R_{3}+R_{4}=215600

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