# Basic physics question

1. Nov 9, 2006

### MattsVai

I am just wondering what is exactly expected when asked "express the answer in terms of g, (acceleration due to earth's gravity). I am thinking it means divide the result by 9.8N? What is the resulting unit?

Any help would be appreciated :)

Cheers

2. Nov 9, 2006

### moose

For example, if you are doing calculations which deal with acceleration due to gravity, instead of putting 9.8 into g in your equations, you simply leave it as g.

So, if you have a formula like mgh = 1/2 mv^2 and you plug in all of your numbers, you would leave your asnwer as something like "5.1g"

So really, if you assumed that you were on the surface of the earth in the problem and you put in 9.8m/s^2 for g, you would divide out 9.8m/s^2 from your answer and replace it with g.

The reason why they may want you to have it in terms of g, is to make it more versatile.

3. Nov 9, 2006

### MattsVai

Ahhhhh.... thanks a bunch! Makes sense :)

4. Nov 9, 2006

### MattsVai

But, what if my equation does not contain any "g" in the formula? Would I then simply divide the final answer by 9.8?

5. Nov 9, 2006

### MattsVai

Sorry... u answered that! I'm just spaced out... thanks again :)

6. Nov 9, 2006

### moose

If you do not have a g anywhere in any of your formulas or equations, you have set up, you would NOT have a g in your answer. It would be pointless.

What I said earlier was that if you already have 9.8 in or whatever, then you can still take it out later.

7. Nov 9, 2006

### MattsVai

But my question is asking to calculate centripetal acceleration (Ac = 4PI^2rf^2) and to express that in terms of g. How would that make sense?

8. Nov 10, 2006

### OlderDan

It makes sense because it allows us to compare other accelerations to the familiar experience of weight. Pilots in high performance jets experience very high centripetal forces in tight turns. It is common to express these forces as "g-forces", and they can run up to 7 to 8 times their weight. They wear special suits to keep the blood from draining out of their heads, and still black out if they stay in such a turn for long. A force of n "Gees" corresponds to an acceleration of a = n*g.