• Dimensional Analysis & Errors
• Motion In One Dimension
• Motion in 2d and 3d (Including Projectile Motion)
• Laws Of Motion
• Work, Power and Energy
• Circular Motion & Rotational Motion
• Gravitation
• Properties of Matter-Solids/Liquids/Gases
• Heat & Thermodynamics
• Simple Harmonic Motion
• Waves
• Electrostatics
• Current Electricity
• Thermoelectric, Heating, Chemical & Magnetic Effect Of Current
• Magnetism and Earth Magnetism
• Electromagnetic Induction, A.C. Circuits, Electrical Devices & Em Waves
• Wave Optics and Ray Optics
• Modern Physics
• Semi-Conductor Devices
• Communication

The definition of speed is :- Speed = Distance/Time

The best way to imagine a situation in which several physical quantities are changing, is by drawing a graph. To picture the behavior of the speed of an object, we plot the distance (from the top of the equation for speed) on the vertical axis and the time (from the bottom of the equation for speed) on the horizontal axis. The result is something like this :

Here, the total distance traveled (y) divided by the time taken (x) is the gradient of the slope. This is also equal to the average speed of the object - remembering that :

In this case, the speed is constant as the slope of the distance-time graph is constant.

By re-arranging the equation we can plot slopes of either distance, or time, on a graph to find their values. For example, we can see how to find the distance from a speed-time graph by rearranging to get :

We then plot a speed-time graph as shown below :

The blue rectangle has an area equal to the speed multiplied by the time. We can see from the equation above, that this is equal to the distance traveled.

Displacement is a vector quantity that describes a distance moved, in a particular direction. The change in an object's displacement with time is called velocity :

We can produce a displacement-time graph to illustrate an object's velocity. Study the following example of a displacement-time graph.

Example
The graph below describes the motion of an ice hockey puck traveling in a straight line and at a constant speed towards the goal.

Here, the velocity of the ice hockey puck is given by:

As before, we can re-arrange the equation, using the two quantities, on the same side of the equation, as axes, to find out the quantity on the other side. Now you have all the skills required to try these examples involving motion at constant speed or velocity.