### Instruction: What is the difference between speed and velocity?
### Response: Speed and velocity are different terms. Speed is a measurement of distance over time. Velocity is a measurement of distance over time in a direction. Speed is scalar and can only be positive. Velocity is a vector and can either be positive or negative. For example, an object moving at a speed of 50 km/h tells us only how quickly it is moving but not its direction. An object with a velocity of +50 km/h tells us its speed and that it is moving forwards. Conversely, an object with a velocity of -50 km/h tells us its speed and that it is moving backward.