When an object travels with a constant velocity of v over a time period of t , the displacement, d , for the object can be calculated using the following equation:. Here is an example of that calculation:. The above equation could be rearranged using algebra into other forms.
Here are all of its forms:. Often the velocity of an object is not constant. It can change as time passes. When this happens, you can calculate an average velocity for the object. So you can notice an acceleration, and the lurches of acceleration we've introduced.
Examples we've picked so far might suggest the following effects of an acceleration:. CharList You're noticed to slow down. You're noticed to speed up. You're noticed to be moving in a new direction. You might also find it useful to match the three categories speeding up, slowing down and changing direction to examples of your own.
That's quite some claim, and a significant synthesis, so we'll spend some time exploring the idea. We've already met acceleration, in episode 1, as a consequence of force acting on mass. Lots of physical quantities have units like this, and so can be thought of as instructions to accumulate. In this topic this pattern of accumulation is particularly important. This is the first of many meetings. The first of Sir Isaac Newton's Three Laws of Motion, which form the basis of classical mechanics, states that an object at rest or in a state of uniform motion will remain that way indefinitely in the absence of an external force.
In other words, a force is that which causes a change in velocity, or acceleration. The amount of acceleration produced on a object by a given force is determined by the object's mass. When physicists speak about an object's velocity, they are talking not only about the object's speed but also about the direction in which it's moving. Similarly, force has a directional component as well as a quantitative one -- a force directly opposing an object's velocity has a different effect on the object than a force acting at right angles to its motion.
In mathematical terms, force, velocity and acceleration -- which is the rate of change of velocity produced by a force -- are "vector" quantities, which is a term that implies their directional component. The easiest way to understand how a force alters an object's velocity is to imagine that force acting in the same direction as the velocity. For example, the jet engines on an airplane provide a force that acts in the direction of the airplane's motion, giving it a positive acceleration and making it go faster.
Air friction, on the other hand, directly opposes the airplane's motion and decelerates it; if the engines stop working, the airplane will fall out of the sky. But when the force of the engine and the upward thrust of air pressure on the aerodynamically designed wings balance the force of friction and other decelerating forces, including gravity, the airplane flies at a constant velocity toward its destination. The gravitational attraction that the sun exerts on the Earth is an example of a force with an important directional component.
Because the gravitational force acts at right angles to the Earth's motion, it doesn't change the speed at which the planet travels, but it constantly changes the direction.
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