# Homework Help: New at Physics, PLEASE HELP

1. Sep 29, 2011

### LanaStClair

New at Physics, PLEASE HELP :)

Hello, I'm in 8th grade advanced Science, we just started physics but I'm very confused. Can anybody help me on how to calculate acceleration and magnitude? Thanks This is NOT homework, I am just trying to study for an exam tomorrow.

Last edited: Sep 29, 2011
2. Sep 29, 2011

### spacelike

Re: New at Physics, PLEASE HELP :)

Well magnitude is a general property of vectors. Not just acceleration.
For example. velocity is a vector, the difference between "velocity" and "speed" is that "velocity" has a magnitude and a direction, whereas "speed" only has magnitude.

So "magnitude" is like the length of the vector. Another way to look at is is that if you are doing 1-dimensional problems (which you probably are) then your "vectors" are basically just a single number that can be positive or negative, then "magnitude" is like the absolute value.

As for acceleration, just think of it as the change in velocity over time.
$$a=\frac{\Delta v}{\Delta t}=\frac{v_{f}-v_{i}}{\Delta t}$$

3. Sep 29, 2011

### GrantB

Re: New at Physics, PLEASE HELP :)

Hello :)

Acceleration is a rate of change of velocity, where velocity is a rate of change of position.

If I run in a 100m race, and finish in 10 seconds, my velocity is how fast I go from beginning to end. In this case it is:

$v = \frac{finish-start}{time} = 10m/s$

In this case, the start is the x=0 position, and finish is the x=100 position.

Acceleration is similar to this.

If I start by going 5m/s and end at 15m/s, then my acceleration is:

$a = \frac{final velocity - initial velocity}{time} = \frac{15m/s-5m/s}{10s} = 1m/s^2$

Now, all of these are averages for the given example, and I randomly chose numbers.

Also, these are all magnitudes. If I were to attach a direction to the magnitude, it would become a vector.

Hope this helps.

4. Sep 30, 2011

### Staff: Mentor

Re: New at Physics, PLEASE HELP :)

While a body is undergoing a change in speed, or even just a change in direction, then it is accelerating (or decelerating).

Only if it is travelling at a constant speed AND in a straight line is it NOT accelerating.

Something going around and around on a circular path at a constant speed is constantly accelerating, since for no time interval is it seen to be travelling in a straight line.

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