Distance, Displacement, Speed and Velocity
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Distance and displacement both refer to movement, but they are not the same. Distance is a scalar quantity that just tells you how much ground an object has covered, regardless of direction. On the other hand, displacement is a vector quantity that not only states the length of the path but also the direction an object has moved from its initial to final position.
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Speed refers to how fast an object is moving, regardless of its direction. It is a scalar quantity, meaning it only represents magnitude and not direction.
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A calculation of speed involves the division of distance covered by the time taken. It can be expressed in various units such as metres per second (m/s), kilometres per hour (km/h), or miles per hour (mph).
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Velocity, like displacement, is a vector quantity. It gives both the speed of an object and its direction of movement. The formula to calculate velocity is displacement divided by time taken.
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Keep in mind that constant speed means the speed is unchanging. That is different from a constant velocity, which implies that an object moves at a constant speed in a constant direction.
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Acceleration comes into play when there is a change in velocity. This could be as a result of changing speed or changing direction. It's calculated by dividing the change in velocity by time taken for the change.
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A positive acceleration means an increase in velocity whereas a negative acceleration (deceleration) represents a decrease in velocity.
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Remember: whilst you may be moving at a high speed, if your direction is changing, your velocity is as well. For example, when you're spinning in a circle, your velocity is constantly changing, even though your speed might remain constant.
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Graphical representations are useful in illustrating distance-time and velocity-time relations. A steep gradient in a distance-time graph indicates a high speed, while a horizontal line suggests no movement. On a velocity-time graph, a steep gradient represents high acceleration, while the gradient itself gives the value of acceleration. The area under the graph gives the displacement of the object.