# Projectiles 1 - Components of Motion

[Lab Index]

BHS -> Staff -> Mr. Stanbrough -> AP Physics -> Kinematics -> this page

In this simulation, you can compare the motion of a projectile with its horizontal and vertical components. Here is how to set it up:

## Part 1 - Horizontal Launch - The Basic Simulation:

1. Open the Interactive Physics program.
2. Create 3 circle objects (). One will be the projectile, one will be the vertical (free fall) component, and the third will be the horizontal (constant velocity) component.
3. Add velocity vectors to all three objects.
4. Add a vertical force to push upward on the center of mass of Mass[3].
5. You want all three objects to start from the same position, but Interactive Physics will object to overlapping objects in this way. You need to tell the program not to worry about collisions between these objects. Here's how:
1. Select all 3 circles. (You can shift-click or select "Select All" from the edit menu, or press <Apple><A>.)
2. From the Object Menu, select "Do Not Collide".
6. Open the Properties Window for Mass[1]. (This is the projectile) Set:
1. x = 0.0 m
2. y = 0.0 m
3. vx = 15.0 m/s
7. In the Properties Window for Mass[2] (this is the free-fall object), set:
1. x = 0.0 m
2. y = 0.0 m
8. In the Properties Window for Mass[3] (this is the constant velocity object), set:
1. x = 0.0 m
2. y = 0.0 m
3. vx = 15.0 m/s (same as object 1)
4. mass = 1.0 kg
9. In the Properties Window for the force (Constraint[5]), set:
1. Fx = 0.0 N
2. Fy = 9.81 N
10. Zoom out () a couple of times, and move the objects to the upper-left corner of the workspace using the scroll bars at the right and bottom of the window.
11. Try a test run.

## Some Improvements:

1. To make the positions of the three balls easier to see, go to the Workspace submenu of the View Menu, and select "Grid Lines".
2. It would be really nice if the three objects left a track of their motion. This is easy to handle in Interactive Physics. In the Tracking submenu of the World Menu, select "Every 32 Frames".
3. To show the components of the velocity vectors, go to the Define Menu and select "Vector Display..."
1. Check the "X" box for the x-component.
2. Check the "Y" box for the y-component.

## Run It!

Run the simulation. Stop it frequently to check the positions and velocities of the three objects, and be sure that you understand the relationships between the motion of the projectile and the free-fall ball and the projectile and the constant-velocity ball.

You can erase the tracks by selecting "Erase Track" from the World Menu, or pressing <Apple><E>.

Look at different starting velocities (be sure that Mass[1] and Mass[3] start with the same vx, though.) Play around with the tracking, etc.

Use the text tool () to add your name to the workspace and make printouts of your favorite runs. Write a short paragraph explaining the relationships between the positions, velocities, and accelerations of the three balls.

## Part 2 - Launch At An Angle

This simulation is very easy to modify to launch the projectile at an angle. Here's a method:

1. Use the scroll bars on the view window to move the three balls to the lower-left corner of the window.
2. Use the Properties Window to give Mass[1] (the projectile) and Mass[2] (the free-fall ball) vertical velocities of 15 m/s (vy = 15 m/s).

## Run This One!

Like the previous version of the simulation, stop it frequently to study the relationships between the positions and velocities of the three balls. Also, explore different horizontal and vertical velocities. (Keep in mind that vx must be the same for Mass[1] and Mass[3], and vy must be the same for Mass[1] and Mass[2].) Make printouts of your favorite runs. Write a short paragraph about the relationships between the positions, velocities, and accelerations of the three balls in this situation. How does this situation compare to the horizontal-launch one?

[Lab Index]

BHS -> Staff -> Mr. Stanbrough -> AP Physics -> Kinematics -> this page
last update June 18, 2000 by JL Stanbrough