Honors Physics Lab – Projectile Motion

GENERAL OPERATION OF THE LAUNCHER:

The PASCO mini launcher will be used for this experiment. Be sure to WEAR SAFETY GLASSES when operating this launcher or when others are operating this launcher. Be safe and always assume the barrel is loaded. Use a C clamp to fasten the launcher to the end of the table as shown below. Aiming is achieved by loosening the thumb screw and rotating the launcher to the desired angle above or below the horizontal as indicated by the plumb bob and protractor on the side of the launcher. When the angle has been selected, gently tighten the thumb screw. Do not over tighten or damage may occur to the ridges on the extruded barrel.

THE EXPERIMENT:

The goal is to verify the properties and relations expected of a projectile moving under the sole influence of gravity. The muzzle velocity of the launcher will be determined by shooting it horizontally off the edge of the table. This muzzle velocity will then be used to calculate the motion of the ball when the launcher is fired at an angle and comparisons will be made to measurements of the observed trajectory.

Part A - Determining Muzzle Velocity – the Horizontal Launch

1. With the launcher clamped near one end of the table, adjust the aim of the launcher to zero degrees so the ball will be projected in a horizontal trajectory. (See instructions for aiming as given above.)

2. Loading the ball. Always cock the launcher with the ball in the piston. Place the ball in the barrel. Push the ball down the barrel with the pushrod until the trigger catches the piston. One audible click indicates that the piston is cocked in the shortest range setting, two clicks indicate the medium range and three clicks set the piston in the long range position. For this experiment use the long range position.

3. Fire one shot to locate where the ball hits the floor. At this position, use masking tape to attach a piece of construction paper to the floor in such a manner that its length is parallel to the direction of the projectile’s motion. When the ball hits the paper it will leave a mark or indentation. Fire several shots.

4. Measure the vertical displacement from the bottom of the ball as it leaves the barrel (this position is marked on the side of the barrel) to the floor. Record this value – the vertical displacement the ball from launch to impact. This shows how far the ball falls.

5. From the point on the floor directly below the release point (shown on the side of the barrel), measure the range (horizontal displacement traveled by the ball) for each shot recorded on the paper target.

6. Find the mean of the range. Record this information and proceed to calculate the time of flight and initial velocity of the ball using this mean value. Show all work in the space provided.

Part B – Range of Projectile Launched at a Nonzero Angle

1. Reposition and clamp the launcher to one end of the table, adjusted so that the ball will land on the tabletop instead of the floor.

2. Adjust the launcher to launch at an angle between 20 and 60 degrees, but not 45º, above the horizontal. Record the angle.

3. Use the magnitude of the muzzle velocity that you calculated in Part A and the launch angle to calculate the horizontal distance (range) for the projectile fired across the table. Assume that the ball lands at the same level as it is launched (and make sure that the launcher is arranged for this to happen). Show all work in the space provided.

4. Measure this predicted range across the table and tape the construction paper so that you can record the impact.

5. Make several shots and measure and record the actual range of the projectile by its impact on the paper target. Repeat several times to get an average value.

6. Shoot the ball at the compliment of the chosen angle and measure the resulting range for a few trials. (Complimentary angles add up to 90º.)

7. Shoot the ball at a 45º angle several trials. Measure the range to verify that it travels farther than at the other two angles tested.

Part C – Range of Projectile Launched at an Angle Over Uneven Terrain

1. Rearrange the launcher to fire from the table’s edge so that the ball will land on the floor. Choose a convenient angle for launching.

2. Measure and record the vertical displacement of the ball (same as done in Part A).

3. Repeat the steps of Part B and predict and then measure the range of the ball. However, this time also use a stopwatch to measure the time in the air.

Questions

1. For Parts B and C: Calculate the percent difference between each mean range and its corresponding predicted range.

2. For Part C: Calculate the percent difference between the mean time of flight and the predicted time.

3. How well do you think the results of this experiment support the equations and concepts of projectile motion? Explain and support your answer by referring to your results.

4. Discuss error. What are the signs and indications that error occurred? What are the most likely sources of those errors that are evident? Remember to consider both random and systematic error.

Your report (30 pts.) shall consist of the following material – neatly labeled and in this order:

q Completed data/calculations tables (22)

q Answers to questions 1 – 4 (8)

Data/Calculations

Part A – Projectile Launched Horizontally

Vertical Displacement

Measured Range Values

(several trials)

Mean Range

Calculated time of flight:

Calculated initial velocity (muzzle velocity):

Data/Calculations

Part B – Projectile Launched at an Angle Over Level Surface

Angle of Launch: _____________

Predicted Range:

Measured Range Values (several trials)	launched at angle shown above	launched at compliment	launched at 45°
Mean Range

Data/Calculations

Part C – Projectile Launched at an Angle Over Uneven Terrain

Angle of Launch: _____________

Vertical Displacement: _____________

Predicted Time and Range:

Measured Values (several trials)	Time of Flight	Range
Mean Time and Range: