# UMass Amherst PHYSICS 131 - Physics 131 Lab Report 1 (4 pages)

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## Physics 131 Lab Report 1

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- Pages:
- 4
- School:
- University of Massachusetts Amherst
- Course:
- Physics 131 - Intro Physics I

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Free Fall Experiment Thursdays 9 00 AM ILC S110 June 1 2017 Abstract In this experiment we measured the position and velocity of a golf ball in free fall The time elapsed and position at the points of free fall as well as the velocity of each is graphed Our objective was to calculate the acceleration of gravity which we calculated as 10 2 m s 2 So we could conduct a reaction time experiment where we would be able to calculate the time it took for a subject to catch the ruler when dropped based on the gravity value we had previously found and the point on the ruler in cm that the subject caught it at Questions Answers 1 When you first observed the data of position vs time the parabolic curves open upward not downward Explain why The parabolic curve opens upwards because it shows where the golf ball is at a point in time since it is in free fall and we are dropping it from above it starts at the highest point and falls downwards to the table and then upwards again as it bounces off the table creating an open upwards parabola 2 Plot a graph of velocity versus time for your data What does the slope of this graph physically represent Your data points should form a straight line What does this signify The slope of this graph represents the acceleration constant of gravity for our slope we got m 10 2 m s 2 The straight line signifies to us that the number for gravity is not changing throughout the experiment Figure 1 shows the velocity graph the red line indicates which points we used to find the slope 3 Is the free fall acceleration constant Based upon the plot of velocity vs time how do you know it is constant Yes the free fall acceleration is constant This is a measurement of the force of gravity on earth which does not change unless something else is acting on it Since in this experiment the only force is gravity it remains constant throughout by looking at the graph you can see that each of the lines have the same or close to the same slope Figure 2 shows the slopes in red of each peak which corresponds to each time the ball fell and bounced back up 4 When the ball bounces off the floor and is moving upward is it still in free fall Explain why Yes the ball is still in freefall because the only force that is acting on it is gravity which allows it to bounce back up The ball is considered to be in free fall until another force besides gravity acts upon it or it stops moving 5 Is it possible for the ball s velocity and acceleration point in different directions Describe in your graph of velocity vs time when this would occur It is possible for the ball s velocity and acceleration to point in different directions i e one be negative and one be positive In the velocity vs time graph when the ball is dropped the line goes downwards and eventually goes below 0 thus indicating a negative velocity but when it is in the process of bouncing back upwards the line is moving up indicating a positive acceleration even though the velocity is still negative Figure 3 shows the velocity vs time graph with a green line to show that below this the velocity is negative and a red line to show the increasing acceleration while velocity is still negative 6 Are there moments when the ball s velocity is zero Is the ball still accelerating Explain why Yes at the ball s maximum height and minimum height the velocity is equal to 0 Even at these point the ball is still accelerating there is always acceleration since gravity is a constant force and during no point of the experiment did we turn gravity off Also hypothetically if velocity 0 and acceleration 0 the ball would stop moving even in mid air at the maximum height which did not occur 7 Calculate the percent error for your result State and explain at least two sources of error for this experiment How might you change the experiment to reduce the error from one of those sources The percent error of our experiment was 064 m s 2 this error could come from the ball not being dropped at a perfectly straight angle causing some shift in the sensors ability to capture the ball s path of motion or if the subject dropping the object applied any additional force onto the object leading to the balls rates and times being effected by something other than gravity We could change the experiment to include a mechanism of dropping the ball such as a base the ball would sit on aligned under the sensor that would retract backwards quickly causing the ball to drop without the worry of a person accidently adding force to it 8 What is your average reaction time What is the uncertainty 2 point 2 Using the equation y t y i v i t gt 2 and the knowledge that initially y i and v i would equal 0m and 0 m s respectively the y t values we collected from where on the ruler the participant grabbed in cm and our g value obtained in the golf ball experiment we were able to solve for 20 different reaction times The average reaction time is 1 26 seconds The uncertainty is 0722 seconds 9 Your lab TA makes a wager with you She holds a 100 bill between your thumb and finger and says you can keep the 100 bill if you can catch it when it drops The bill is 15cm long Using your reaction time do you catch the bill Explain 2 points 2 Yes because by using the same formula of y t y i v i t gt 2 and the knowledge that y t 15 cm y i 0 m v i 0 m s and g 10 2 m s 2 we can solve for t which 1 714 seconds meaning in that time the bill would slip in between my thumb and finger to the ground however since my average reaction time is 1 26 I would catch the bill at about 8 09 cm since y t 10 2 1 26 2 2 8 09 Conclusion This experiment helped us learn how to manipulate the free fall equation to find time or position using initial velocity initial position and gravity as our acceleration Using it we were able to see how an object falls and the time that must elapse to reach a certain position

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