Since we are dealing with motion in a straight line, direction will be indicated by sign — positive quantities point one way, while negative quantities point the opposite way.
Determining which direction is positive and which is negative is entirely arbitrary. The laws of physics are isotropic ; that is, they are independent of the orientation of the coordinate system. Some problems are easier to understand and solve, however, when one direction is chosen positive over another. As long as you are consistent within a problem, it doesn't matter. The relation between velocity and time is a simple one during uniformly accelerated, straight-line motion.
The longer the acceleration, the greater the change in velocity. Change in velocity is directly proportional to time when acceleration is constant. If velocity increases by a certain amount in a certain time, it should increase by twice that amount in twice the time. If an object already started with a certain velocity, then its new velocity would be the old velocity plus this change. You ought to be able to see the equation in your mind's eye already.
This is the easiest of the three equations to derive using algebra. Start from the definition of acceleration. This is the first equation of motion. It's written like a polynomial — a constant term v 0 followed by a first order term at. Since the highest order is 1, it's more correct to call it a linear function.
It is often thought of as the "first velocity" but this is a rather naive way to describe it. A better definition would be to say that an initial velocity is the velocity that a moving object has when it first becomes important in a problem. Say a meteor was spotted deep in space and the problem was to determine its trajectory, then the initial velocity would likely be the velocity it had when it was first observed.
But if the problem was about this same meteor burning up on reentry, then the initial velocity likely be the velocity it had when it entered Earth's atmosphere. The answer to "What's the initial velocity? This turns out to be the answer to a lot of questions.
The symbol v is the velocity some time t after the initial velocity. It is often called the final velocity but this does not make it an object's "last velocity". Take the case of the meteor. What velocity is represented by the symbol v? If you've been paying attention, then you should have anticipated the answer. It depends. It could be the velocity the meteor has as it passes by the moon, as it enters the Earth's atmosphere, or as it strikes the Earth's surface.
It could also be the meteorite's velocity as it sits in the bottom of a crater. Are any of these the final velocity? Who knows. Someone could extract the meteorite from its hole in the ground and drive away with it. Distance: Distance is how far or how much ground has been covered by an object. Distance is a scalar quantity. Distance and displacement Displacement: Displacement is the change in position of an object. Displacement is a vector quantity. Speed: Speed is a scalar quantity and does not measure direction.
Because, since acceleration is defined as the change in velocity, and there is no change in velocity, the acceleration is actually zero. You can see all of these comparisons in this graph if you don't know calculus yet, you can just focus on the diagram -. How are acceleration, time and velocity related? Physics 1D Motion Acceleration. Jun 10, An object uniformly accelerates from What is the rate of What is its However, acceleration is the key characteristic here, not velocity.
The equation for momentum uses velocity instead of acceleration. Their definitions are different, and this shows how those differences lead to distinct equations in practice.
Lee Johnson is a freelance writer and science enthusiast, with a passion for distilling complex concepts into simple, digestible language. He's written about science for several websites including eHow UK and WiseGeek, mainly covering physics and astronomy.
He was also a science blogger for Elements Behavioral Health's blog network for five years. He studied physics at the Open University and graduated in How to Determine Magnitude of Velocity. How to Calculate a Change in Momentum.
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