Displacement and Distance Aren’t the same thing?

Position In physics, the word position refers to the location of an object at one instant. A position is always specified relative to an origin. The net change in position relative to the origin is called displacement.

Distance Distance is related to, but different from, position. Distance is a measure of length without regard to direction.

Speed and Distance Speed is the rate at which distance changes. In science, the word rate means the ratio of how much something changes divided by how long the change takes. Constant speed means the same change in distance is traveled every second.

Speed is a Measure of Change in Position The change in position is a distance traveled in a given amount of time. To calculate the speed of an object, you need to know two things: the distance traveled by the object the time it took to travel the distance Since speed is a ratio of distance over time, the units for speed are a ratio of distance units over time units.

Units of Speed

Calculating Speed A bird is observed to fly 50 meters in 7.5 seconds. Calculate the speed of the bird in m/sec. 1.You are asked for speed in m/s. 2.You are given distance = 50 m; time = 7.5 s 3.Use v = d ÷ t

Velocity is Different from Speed The velocity of an object tells you both its speed and its direction of motion. A velocity can be positive or negative. The positive or negative sign for velocity is based on the calculation of a change in position. Two cars going opposite directions have the same speed, but their velocities are different—one is positive and the other is negative.

Calculating Velocity Velocity is the change in position divided by the change in time.