Acceleration and velocity

Let's Review... Imagine that you're in a car traveling at a high speed and accelerating quickly. You're heading directly toward a brick wall, and you continue to accelerate until you reach that wall. Sounds like you're in a heap of trouble, doesn't it? Not necessarily. When we hear the word acceleration, we usually assume it means "increasing in speed." In many cases, that's exactly right. But in physics, acceleration is defined as "a rate of change of velocity." This change can be either an increase or a decrease in speed, or a change in direction. In the example given here, acceleration refers to a decrease in speed, so the car decelerates as it approaches the brick wall, slowing down until it gently bumps into it. Define "acceleration." What does it mean besides an increase in speed? Speed and Velocity Just as acceleration has a precise meaning in physics, so do the terms speed and velocity. While it's perfectly acceptable at times to use the two terms interchangeably, each can have its own distinct meaning. Speed is defined as the rate of motion and is calculated by dividing the distance an object travels by the time it takes to travel that distance. Velocity, on the other hand, is a vector quantity -- a measurement of both the rate of motion (i.e., speed) plus direction. In other words, ten kilometers per hour is speed; east at 10 kilometers per hour is velocity. Match the terms with their definitions below. Acceleration rate of change of velocity rate of motion plus direction Velocity Speed rate of motion (distance / time) Acceleration and Circles... It's possible for an object to be moving at a constant speed and be accelerating at the same time. Take as an example a car driving in a circle at 30 kilometers per hour. Although its speed is constant, its velocity is continually changing because its direction is continually changing as well. This change of direction results in an acceleration toward the center of the circle. Likewise, a satellite in circular orbit around Earth is traveling at a constant speed and accelerating toward Earth's center. When a horse in running in a circle, it’s continuously accelerating, even though it may not seem like it. Even though the horse’s speed is constant, it’s accelerating because it’s changing direction. It’s the same as when you’re running in a circle. When you run in a circle, you can feel your foot pushing on the ground. Your foot pushes in the opposite direction that you want to turn. That’s because the ground will push back with a force in the direction you actually want to go.