Simple Determination of Initial Velocity of a Pojectile

In summary, there are several methods that can be used to determine the initial velocity of a projectile, including shooting the projectile horizontally and using the range to calculate velocity, catching the projectile in a swinging catcher and using conservation of energy and momentum, keeping track of the recoil, using two gates at a known distance apart, using a strobe light and camera, or using sound and measuring the reflected doppler shift. These methods can be utilized with common physics classroom tools such as a digital camera, photogates, and a backdrop with a scale and axes. It is important to keep track of the path of the projectile when using these methods.
  • #1
Chrishaum
3
0
Simple Determination of Initial Velocity of a Projectile

It is possible to roughly determine the initial velocity of a projectile shot from a launcher like the one linked to below using a number of methods.

http://www.science4schools.co.uk/acatalog/10-1365.jpg [Broken]

Two of which I am aware are:

(1) shooting the projectile horizontally and using the range to calculate the initial velocity and

(2) catching the projectile in a foam block (free to swing) immediately after it is fired and using the change in height to calculate the initial velocity with conservation of energy and momentum. Here is the swinging catcher: http://www.science4schools.co.uk/acatalog/10-1368.jpg [Broken]

The first method seems to be more accurate, but it takes longer than the second method.

What fast, accurate methods are there for determining the initial velocity, utilizing common physics classroom tools?
 
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  • #2
Actually, you're not guaranteed that the projectile will stop moving -- it could, for example, go into orbit. You need to keep track of the path to use this method in general.

A method that would work is to keep track of the recoil.

Two gates at a known distance apart is fairily popular and effective.

Alternatively, a strobe light and a camera would give you two locations separated by a known amount of time.

A more sophistcated approach would be to use sound and measure the reflected doppler shift.
 
  • #3
Thank you for your responses, NateTG.

My end goal in determining the initial velocity is to utilize it in repudiating the following equation for projectile motion:[tex]y = (tan \theta_0)x - \frac{gx^2}{2(v_0 cos \theta_0)^2}[/tex]

As my experiment stands, a digital camera will capture the trajectory of the ball in a rapid series of photographs. A backdrop behind the path will be marked with a scale and horizontal and vertical axes (with the tip of the projectile launcher being the origin). I will then be able to use an imaging program to find the ball's x- and y-values along the path.

Following your suggestion, I will place two photogates near the origin to find the initial velocity. I thought about finding the distance the ball travels between the first two frames and dividing by the time between the camera's shots. However, this would be less accurate than using the photogate method.
 

What is the "Simple Determination of Initial Velocity of a Projectile"?

The "Simple Determination of Initial Velocity of a Projectile" is a scientific method used to calculate the initial velocity of an object that has been launched into the air, such as a projectile or a ball. This method uses the equations of motion and measurements of the object's displacement and time to determine its initial velocity.

Why is it important to determine the initial velocity of a projectile?

Determining the initial velocity of a projectile is important for understanding the motion of the object and predicting its trajectory. This information can be useful in a variety of fields, such as physics, engineering, and sports, where the ability to accurately calculate and predict the motion of objects is crucial.

What are the key components of the "Simple Determination of Initial Velocity of a Projectile"?

The key components of this method include measuring the displacement of the object, recording the time it takes for the object to travel that distance, and using the equations of motion (such as the kinematic equations) to calculate the initial velocity of the object.

What are some common sources of error in determining the initial velocity of a projectile?

Some common sources of error in this method include inaccurate measurements of displacement and time, air resistance or wind affecting the motion of the object, and not accounting for external forces acting on the object, such as friction or gravity.

How can the accuracy of the "Simple Determination of Initial Velocity of a Projectile" be improved?

The accuracy of this method can be improved by taking multiple measurements and averaging them, using more precise measuring tools, and taking into account any external factors that may affect the motion of the object. It is also important to ensure that the object is launched in a consistent manner for each trial.

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