When a ball rolls down an inclined ramp, off the edge of a table, the ball becomes a projectile with some positive horizontal velocity and an initial ...
PROJECTILE MOTION LAB PHYSICS, LA QUINTA H.S. MR. HAVARD (RM. 331) When a ball rolls down an inclined ramp, off the edge of a table, the ball becomes a projectile with some positive horizontal velocity and an initial vertical velocity of zero. However, the length of time that the projectile stays in the air depends not on the horizontal velocity but on the height of the table above the ground. The horizontal velocity determines how far the projectile travels during the time it is in the air. In this lab, you will roll a ball down an inclined ramp, off the edge of a table, and onto a piece of carbon paper on the floor. In this lab students will investigate the flight of a projectile when fired off a table horizontally. The horizontal distance which it flies before it hits the floor will be measured and the experimental initial velocity will be compared to the theoretical initial velocity. OBJECTIVES 1. Measure the velocity of projectiles in terms of the horizontal displacement during free fall. 2. Compare the actual and theoretical velocity of projectiles accelerated down an inclined ramp.
MATERIALS LIST 1. Aluminum Ramp 2. Steel Ball 3. Carbon Paper 4. Meter Stick 5. Tape 6. String
PROCEDURE 1. With a meter stick, measure the height of the end of the ramp above the floor and record this value. 2. Place the ball at the highest point on the ramp where it can still roll down when released. Measure and record the height of the ball above the end of the ramp. 3. Release the ball and note approximately where it lands. Repeat this to make sure that it did not happen by chance. 4. Tape a piece of white paper to the floor with its center approximately where the ball landed. Then place a piece of carbon paper over the white paper.
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5. Roll the ball down the ramp from the top of the ramp. When it hits the floor, it should hit the carbon paper and leave a dot on your white paper. Roll the ball at least five more times down the ramp. 6. Take a piece of string which is long enough to reach the end of the ramp to the floor and tie a washer to it. Hold the string at the end of the ramp so that the washer is just off the floor. Gravity will make the washer hang vertically to show the place which is under the ramp. 7. From this point, measure the horizontal distance to each of the black marks made by the ball on your white paper. Record each value (total of six, one for each trial).
ANALYSIS 1. Find the average distance that each black mark was from under the ramp. Give some estimate of the error in this value. 2. Using the height of the ramp above the floor, find the time for the ball to fall from the ramp to the floor. Assume that the vertical velocity is initially zero. 3. The ball moved horizontally the distance you found in step 1 in the time you found in step 2. Use these values to calculate the ball’s velocity when it left the ramp. 4. Given the following equation to determine the theoretical initial horizontal velocity, find the velocity which the ball was going when it left the ramp:
v=
10a g h 7
Where ag = 9.81 m/s, h = height of ball from the table (on ramp), and v = theoretical initial horizontal velocity.
CONCLUSIONS 1. How does the velocity found by measuring the distance the ball flew and the time it was in the air compare with the velocity calculated by using the theoretical equation above? Can the differences be explained by measurement errors in the lab? Can any other sources of err help cause the differences? 2. Why might using the vertical displacement to calculate the time interval be more reliable than using a stopwatch for each trial? 3. What effect on the lab would there be if the ramp were not horizontal at the lower end? How would you have to change your calculations?
