# Projectile trajectory : calculating gravity and height

• yoziva
In summary, the conversation discusses simulating projectile movement without air friction and finding the formulas for initial angle (θ) and gravity (g) based on given parameters of initial height (y0), initial velocity (v0), maximum horizontal travel distance (d), and maximum height (h). The goal is to launch a projectile at any distance without changing its initial velocity, which requires modifying the gravity in the simulation.

#### yoziva

Hello,

I'm trying to simulate a projectile movement (without any air friction). But my projectile parameters are not conventional.

I know :
1. The initial height (y0)
2. The initial velocity (v0)
3. The maximum horizontal travel distance (d)
4. The maximum height (h)

I need to find :
• the initial angle (θ)
• the gravity (g)

So basicly I'm trying to find the formulas that give θ and g according y0, v0, d, h.
And that's where I'm stuck :)

Here is an image to be a bit clearer :
[PLAIN]http://img14.imageshack.us/img14/6706/projectile.png [Broken]

Any help is welcome

Thanks !

Last edited by a moderator:
Depending on where you are, say Earth at ground level/small heights, 'g' would be 9.81 m/s^2 i.e. a constant. You would know 'g'.

As for θ, if you consider vertical motion,

v2=u2-2gh

at max height, H, v=0 so you would be able to solve for u which would involve the angle θ.

Thanks, but actually I cannot use 'g' with 9.81 m/s^2 or any other 'constant'.

I know it is not usual but 'y0' 'v0' 'd' and 'h' are my constants. 'θ' and 'g' are my variables.

You may consider I'm simulating the projectile on an unknown planet, or if you prefer a planet where the gravity can change between two projectiles throw.

The goal behind that is quite simple actually. In my simulation I want to be able to launch a projectile at any possible distance without changing its initial velocity. So the only way to be able to do that is to modify the gravity (hard to do that on Earth but not in a simulation) And since I also have another constraint, the height. I also need to find 'θ'.

Thanks

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## What is projectile trajectory?

Projectile trajectory refers to the path that a projectile takes when it is launched into the air and travels under the force of gravity.

## How do you calculate gravity?

Gravity can be calculated using the formula F = G(m1m2)/r^2, where G is the gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between them.

## What variables affect projectile trajectory?

The variables that affect projectile trajectory include the initial velocity, angle of launch, air resistance, and the force of gravity.

## How do you calculate the height of a projectile?

The height of a projectile can be calculated using the formula h = v^2(sin^2θ)/(2g), where h is the height, v is the initial velocity, θ is the angle of launch, and g is the acceleration due to gravity.

## What is the importance of understanding projectile trajectory?

Understanding projectile trajectory is important in various fields such as physics, engineering, and ballistics. It allows us to predict and control the motion of objects in the air, which is crucial in designing and optimizing various systems and technologies.