# Practical - Finding the value of gravity

• actionreaction
In summary, the conversation involved setting up an experiment to measure the angle theta (dependent variable) by adding different masses (independent variable) to a setup that resembled an attached diagram. The task was to draw an appropriate graph and determine the value of gravity from the gradient. However, the group had no success and struggled with determining the variables to plot on the graph. After various attempts, the closest result achieved was a magnitude of 7. It was later revealed that a mistake had been made in assuming the tension force of 2N for both strings, which allowed for graphing cos(theta/2) against mass. It was also mentioned that g could not be determined from the given setup and information.
actionreaction
1. We had to set up an experiment that looked like the attached diagram. By adding different masses (independent variable) we would measure angle theta (dependent variable). Our task was to draw an appropriate graph and from the gradient, see what our gravity value came to.

So far i have had no luck and what I am stuck on is the variables being plotted on the graph, as my first graph attempt didn't produce a value close to 9.81m/s^2 or 10N/kg. All I'm asking is if I can have a bit of direction with the variables I am supposed to display on my graph to find the correct value of gravity.

#### Attachments

• lab.jpg
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how much did it produce?

The angle does not depend on ##g##.

I've tried various ways to produce the value of gravity (guess and check method - not ideal but it may help me realize), therefore I have achieved numerous results. The closest I got was a magnitude of 7.

After looking at the problem more carefully, I agree with voko. There is no way to get the value of g from measuring the angle in this setup.

It might have been possible to determine g if the blocks were moving (say the middle mass falling, and the 200 g masses [STRIKE]falling[/STRIKE] rising), and then the time taken for one of the blocks to fall a certain distance were measured. But this setup does not seem to allow for that sort of measurement, and you would probably have wanted the angle to be zero -- i.e., all the strings vertical.

(EDIT: made correction as indicated above.)

Last edited:
actionreaction said:
I've tried various ways to produce the value of gravity (guess and check method - not ideal but it may help me realize), therefore I have achieved numerous results. The closest I got was a magnitude of 7.
Since g cannot be determined from the given setup and information, how did you arrive at any number for g?? For a given hanging mass, theta will be the same whether the experiment is conducted on Earth , Jupiter,, or the Moon.

Yeah I realized the problem. The reason why I still attempted was because I was intrigued why it was so difficult. Anyway, long story short, we were not told until today that a mistake had been made, and we were meant to assume we already knew the tension force of 2N for both strings. From that we can graph cos(theta/2) against mass.

## 1. What is the formula for calculating gravity?

The formula for calculating the force of gravity is F = G * (m1 * m2) / r^2, where G is the universal gravitational constant, m1 and m2 are the masses of the objects, and r is the distance between them.

## 2. How is the value of gravity measured?

The value of gravity is typically measured using a device called a gravimeter, which detects changes in gravitational force. It can also be indirectly measured by measuring the acceleration of objects due to gravity using tools such as a pendulum or a free-fall apparatus.

## 3. What factors affect the value of gravity?

The value of gravity is affected by both the mass and distance between two objects. The greater the masses of the objects, the greater the force of gravity between them. The farther apart the objects are, the weaker the force of gravity will be.

## 4. Why does the value of gravity change on different planets?

The value of gravity is dependent on the mass and size of a planet. Planets with greater mass and larger sizes will have a stronger gravitational force, while smaller planets will have a weaker force. This is due to the fact that the greater the mass and size of a planet, the more it can pull objects towards its center.

## 5. How does altitude affect the value of gravity?

The value of gravity decreases as altitude increases. This is because as you move further away from the Earth's center, the distance between you and the center of the Earth increases, resulting in a weaker force of gravity. This is also why objects weigh less on the top of a mountain compared to at sea level.

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