| Applications and Skills |
|---|
| Discussing the conservation of total energy within energy transformations |
| Sketching and interpreting force–distance graphs |
| Determining work done including cases where a resistive force acts |
| Solving problems involving power |
| Quantitatively describing efficiency in energy transfers |
| Understandings |
|---|
| Kinetic energy |
| Gravitational potential energy |
| Elastic potential energy |
| Work done as energy transfer |
| Power as rate of energy transfer |
| Principle of conservation of energy |
| Efficiency |
Dynamics is the study of forces as they applied on body and how bodies respond to these forces.
Generally, we use a free body diagram to solve the problems and apply Newton’s law.
To use Newton’s law it is necessary to know all of the forces applied on a body.
However, it is sometimes too difficult to for Newton to solve everybody’s problems.
Example: We wish to know the speed of the ball when it reaches the end of the track.
Problem: the slope of the track keeps changing; and so the weight and the reaction force both keep changing.
This type of problems can be solved using the principles of work and energy.
Energy can be stored in many different forms.
| Energy | Nature of energy associated with |
|---|---|
| Kinetic | The motion of mass |
| (Gravitational) potential | The position of mass in a gravitational field |
| Electric/Magnetic | Flow of charge |
| Chemical | Atoms and their molecular arrangements |
| Nuclear | The nucleus of an atom |
| Elastic (potential) | An object being deformed |
| Thermal (heat) | A change in temperature or a change of state |
| Mass | Conversion to binding (nuclear) energy when nuclear changes occur |
| Vibration (sound) | Mechanical waves in solids, liquids, or gases |
| Light | Photons of light |
Energy can be transferred between any of its forms and it is during such transfers we see the effects of energy.
When energy changes from one form to another we find that nothing is lost. This is known as the principle of conservation of energy.
$$ \Delta E_{system} + \Delta E_{surroundins} = 0 $$
The energy of the system may change as a result of interactions with its surroundings. These interactions mainly involve work done W by the surroundings and/or the transfer of thermal energy (heat) Q, to or from the surroundings.
In this section we will deal with Q = 0 and no other transfers:
$$ \Delta E = W $$
In physics, a force is said to do work if, when acting, there is a movement of the point of application in the direction of the force. The work done by a force is defined as:
$$ \text{Work done} = \text{Force exerted} \times \text{distance moved in the direction of the force}\\{}\\ W = Fscosθ $$