Motion: Distance, Displacement, and Speed

Descriptors of Motion

• Motion can be described in terms of distance or displacement, speed or velocity, and acceleration
• Object motion is described relative to something else
• Describing object motion requires a point of reference (reference frame)

Distance and Displacement

• Distance is the length of path travelled by an object
• Displacement is defined as the change in the position of an object from its starting point to its final point
• The total distance travelled by a ball rolled 2 meters to the right, 1 meter to the left and then 2 meters to the right is 5 meters
• The displacement of the ball from its starting point is 3 meters to the right and consider the direction in which the object moves to

Speed

• Speed describes the motion of an object
• Speed measures how far an object travels over time.
• The measurement is distance per unit of time
• A car travels 300 kilometers in 3 hours, you that car's speed is 100 km/hr
• Speed is measured in units like miles per hour and meters per second

Velocity

• Physics distinguishes between speed and velocity, although the terms are interchanged
• Speed is a positive number measuring distance per unit time
• Velocity indicates both the magnitude (numerical value) of how fast an object moves, and direction
• Speed is the distance travelled per unit of time
• Velocity measures displacement travelled per unit of time.

Acceleration

• Objects move at different rates, meaning their acceleration varies.
• The speed of a ball dropped from a certain height varies before it touches the ground
• If a ball is tossed upwards, its speed decreases until it momentarily stops
• “Speeding up” and “slowing down” phenomena, are called acceleration
• Acceleration defines the change in velocity per unit of time
• Acceleration also considers the direction of motion
• Plus (+) and minus (-) signs are used to indicate the direction of the acceleration during one-dimensional motion/motion along a straight line
• The sign is dependent on the motion of the object and point of reference
• The plus sign is used for the positive x direction (rightward motion) and minus sign for the negative x direction (leftward motion).
• Acceleration is in the same direction as velocity if an object is speeding up
• Acceleration is in the opposite direction of the velocity when an object is slowing down

Explore motion through distance, displacement and speed. Understand reference frames and how they relate to motion. Learn how to calculate speed using distance and time, with practical examples.