Understanding Forces and Motion: A Comprehensive Lab Guide

Forces and Motion Carlos Zabaleta February 17, 2024 Prof. Irina Golub

Purpose The objective of this laboratory experiment was to anticipate the impact of an external force on the speed of an object and to examine the connection between unbalanced forces and the overall force acting on the object. The phET Stimulator was employed for this purpose. The experiment involved the manipulation of blue and red figures of different sizes to observe how altering their positions affected the direction of the net force. In the second segment, diverse objects with distinct masses were utilized, and their final velocities were measured over a five-second interval.

Introduction A force is something that can push or pull an object, making it move, altering its direction, or changing its shape. Forces are responsible for the motion and changes in the motion of objects. Gravity and magnetic forces serve as examples of forces that operate from a distance, not requiring direct contact with the objects. Another category is contact forces, and in this lab, we focused on tension force, applied force, and frictional force. These applied forces influence how fast an object moves.

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Procedure Part I: Net Force 1. Click the boxes "sum of forces" and "values." 2. Place a small blue figure and a small red figure on the rope and observe what the net force is. 3. Place another blue figure on the rope and observe the forces and net force 4. Answer the following questions: How can an equilibrium situation be achieved again? Give two possibilities. 5. Fill in the table with the values of the forces and insert screenshots of each scenario into the table as well. Part I: Constant mass, changing force. 1. Select the motion tab on the simulation. 2. Select all the items in the yellow box in the upper right-hand corner. 3. Choose any item from the bottom left/right boxes and place it on top of the skateboard. 4. Set the "Applied Force" to 50 N and observe the motion of the object for 10-15 seconds. 5. Without changing the item on the skateboard, change the applied force to higher values (100 N, 150 N, 200 N), and observe the motion for the object for at least 10 seconds of each value of applied force. Part II: Constant force, changing mass. 1. Click the "reset" button.

2.) Select all of the items inside the yellow box and remove the crate from the top of the skateboard and place it inside the box. 3.) Place the 40 kg child on top of the skateboard and observe its acceleration within a 5 second time interval. 4. Set the force to 50 N. Stop the motion of the body after 5 seconds by pressing the "pause" button. Observe the speed attained by the body after 5 seconds and record this value in Table 1 as the final velocity for the specific item. 5. Perform the same steps for all the other items in the table. And calculate the mass for each object. Select "reset" every time you start with a new item and click all the items inside the yellow box. The force will remain constant (50 N) for all the items. 6. Compute the acceleration for all the items in the table and record the data.

Data and Evaluation Part I: Net Force 1. Click the boxes “Sum of forces” and “Values” 2. Start by putting a small blue figure and a small red figure on the rope. Observe what the net force is. The net force was equal on both sides, 50 N, and the net force was 0 N, after one small blue figure and one red figure were added.

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3. Put another blue and again and observe the forces and the net force. There was more force on the left side than on the right after another blue man was placed. There was a force of 100 N on the left and 50 N on the right. The left side had a net force of 50 N. 4. How can a get an equilibrium situation again? Give two possibilities. Place the necessary figures on both sides, take a screenshot of the simulator for each option you propose, and insert it in the lab report.  You can get the equilibrium by placing the red man on the right side.  Another way you can reach equilibrium is by putting one medium blue figure on the left and two small red figures on the right.

5. Fill in the following table with the values of the forces (some boxes can have more than one possible correct answer). Place the figures you suggest on both sides, take a screenshot of the simulator for each option, and insert it in the table, as shown. Situation Force to the left (N) Force to the right (N) Net force (N, left or right) 50 N 100 N 50 N, right 100 N 100 N 0 N

150 N 250 N 100 N, right 150 N 200 N 50N, right 100 N 150 N 50 N, right 50N 200 N 150 N, right

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200 N 100 N 100 N, left PART I: Constant mass, Changing Force 1. Open the link again and choose the Motion tab: 2. You will see the simulation on “Motion” as shown below: 3. Keep all the items inside the yellow box (upper right-hand corner) ticked.

4. Choose a particular item from bottom left/right boxes and position it on top of the skateboard. 5. Set the “Applied Force” as 50 N (“N” stands for “Newton”, a unit of force) by clicking/tapping on the right arrow once. Observe the motion of the crate within 10-15 seconds. You may look at how fast the value of speed changes, as shown in the circle on the upper left corner. 6. Without changing the chosen item on the skateboard, set the applied force into higher values (100 N, 150 N, 200 N…) by clicking/tapping on the right arrow. Observe the motion of the object for at least 10 seconds for each value of applied force. 7. Carefully notice how fast the value of the speed changes for each value of force applied. 8. What does this observation tell you about the relationship between the external force applied and the object’s acceleration (the rate of change in velocity)? This finding indicates that as the applied power increases, so does the item 's acceleration. This implies that the acceleration of the item and the applied external force directly correlate to one another.

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PART II: Constant force, changing mass 1. Click the “reset” button (the round, orange button on the upper right-hand corner) of the same simulation to clear all the current settings. 2. Tick all the items (force, values, masses, speed) inside the yellow box. Remove the crate from the top of the skateboard and place it inside the box (lower left). 3. Position the 40-kg child on top of the skateboard. You have to observe its acceleration within a 5-second time interval by referring to Step 4. Use a digital stopwatch as a timer. 4. Set the force at 50 N. The skateboard and its load will then start moving. Stop the motion of the body by pressing the “pause” button AFTER FIVE (5) SECONDS (starting from the time you set the force as 50 N). Check the speed (refer to the speed shown in the circle, upper left) reached by the body within the 5-second time interval. Record this value in Table 1 as the final velocity of that particular item. 5. Do the same for all the other items listed in the table below. Click “reset” every time you start with a new item, and always tick all the items inside the yellow box. Remove the crate (the default setting) on top of the skateboard before placing a new item, unless the crate itself is the item you need to select. The force must be the same (50 N) for all these items. 6. Compute for the acceleration of all the items considered and record the data in the last column. The acceleration is equal to final velocity – initial velocity divided by time (time equals 5 seconds for all the items).

TABLE 1: ACCELERATION OF DIFFERENT BODIES AT 50-N FORCE ITEM MASS (kg) INITIAL VELOCITY (m/s) FINAL VELOCITY (m/s) ACCELERATION (m/s 2 ) Girl 40 0 6.8 1.36 Crate 50 0 5.8 1.16 Man 80 0 3.6 0.72 Girl + Crate 90 0 3.3 0.66 Trash can 100 0 2.7 0.54 Man + Crate 130 0 2.4 0.48 Crate + Trash can 150 0 1.8 0.36 Man + Trash can 180 0 1.6 0.32 Refrigerator 200 0 1.3 0.26

7. What did you notice with the acceleration values obtained by the different items? What do you think caused the variations in these values? I saw that the values started to decrease as the mass increased and the final velocity decreased. This is primarily caused by the mass which heavily influences the velocity of an object.

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Conclusion In summary, we found a link between the force acting on an object and its motion. Objects tend to move more slowly if they are heavier, as demonstrated in part II where the final velocity decreased with the increased weight of the items on the skateboard. Newton's second law explains the relationship between force and acceleration. The size and direction of the net force directly impacts an object's acceleration.

Resources Urone, Paul P., and Roger P. Henrich. " Unit 3: Forces and Newton's laws of motion" College Physics, OpenStax, 2012 https://www.khanacademy.org/science/physics/forces-newtons-laws

Forces and Motion

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