Force Lab 3

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Physics

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Oct 30, 2023

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Breana Aguilar PHY-10-0752 30 September 2023 FORCE AND NEWTON’S LAWS REVIEW To Begin: https://phet.colorado.edu/en/simulations/forces-and-motion-basics Part I - Newton’s First Law Choose the “Motion” window to start the simulation. Make sure the boxes that say “Force”, “Values” and “Speed” are checked! a. Apply a force of 50 N right to the box. Describe the motion of the box using physics terms (i.e., velocity, acceleration, displacement). Refer to the speedometer in your answer. a The velocity of the box is increasing to the right as the speedometer shows an increasing number. The acceleration is constant, to the right, and displacement is increasing, to the right. b. Reset the scenario (don’t forget to check forces, speed again). Apply a force of 50 N to the right for about 5 seconds then reduce the applied force to zero (the man should stop pushing). Don’t reset the scenario. Describe the motion of the box. Refer to the speedometer in your answer. a The velocity of the box is constant, as the speedometer shows the same number. The acceleration is zero and the displacement is increasing to the right . c. Apply a force of 50N to the left. Describe the motion of the box. a The velocity of the box is increasing to the left as the speedometer shows an increasing number. The acceleration is constant and to the left, the displacement is increasing to the left. d. Explain the exact steps needed to make the box come to a stop. a To make the box come to a stop, a force would need to be applied in the opposite direction of the motion, so the speedometer reaches 0 m/s. Summary Newton’s First Law of Motion States “An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.” Explain how your observations in a - d support this, Law. When there is no force applied to the box, the box won’t move. If there is a constant force applied to the box, the box will move with increasing velocity. If there is a force applied for a short time interval, the box will continue to move with constant velocity.

Breana Aguilar PHY-10-0752 30 September 2023 Part II - Newton’s Second Law a. Reset the sim, don’t forget to check force, values, and speed again. Remove the box and place a garbage can on top of the skateboard. Using your timer/phone, measure the amount of time it takes to reach maximum speed using a force of 50 N. Try this again with forces of 100N, and 200N. Applied Force (N) Time To Max Speed (s) 50 97 seconds 100 40 seconds 200 20 seconds b. Reset the sim, check force, values, speed, and the masses boxes this time. Set the applied force to 200 N Right. Using your timer/phone measure the amount of time it takes to reach maximum speed. Repeat with two crates, one crate and a garbage can, and a refrigerator. Record your findings! Object – Mass (kg) Time To Max Speed (s) 50 10 seconds 100 20 seconds 150 30 seconds 200 40 seconds Create a graph of time vs mass. Sketch this graph in the space below. Recall how acceleration is related to time (a = v/t). Note: In this case the final speed of all the trials is the same (so the v in a = v/t should be the same value every time you calculate a for every value of t). Sketch an acceleration vs mass graph using this data in the space below.

Breana Aguilar PHY-10-0752 30 September 2023 Summary Newton’s Second Law states “The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.” Explain how your observations in both a and b support this, Law. The heavier the object, the longer it will take to accelerate to a certain speed. The larger the force applied, the larger the acceleration. Part III - Friction’s Effects The behavior of the skateboard in Part I and part II were not very realistic because friction was not present. At the bottom of the screen is a simulation that includes friction. Select this simulation. a. Set friction to “none”. Notice how the screen changed. Why do you think the app designers did that? a The ground changes to ice because different surfaces have different amounts of friction. b. Make sure that only speed box is checked. i. Apply a force to get the box to about half of its maximum speed, then remove the force. ii. ii. While the box is moving, move the friction slider to 1/2 way. What happened to the box? 0 5 10 15 20 25 30 35 40 45 50 100 150 200 Object Mass (kg) Time to Max Speed (s) Time vs Mass Graph

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Breana Aguilar PHY-10-0752 30 September 2023 The box began to slow down and eventually came to a stop. Summary Is friction a force? What evidence do you have? Friction is a force because it caused the box to slow down and come to a stop, which meant that the friction force was acting in the opposite direction of the motion. Part IV - Back to Newton’s Second Law Reset the Friction app. Make sure Forces and Speed are checked. a. Apply a force of 50 N. Describe the movement of the box. a The box doesn’t move as the friction force encounters the applied force of 50 N. b. Apply a force of 100 N. Describe the movement of the box. a The box doesn’t move as the friction force counters the applied force of 100 N. c. Apply a force of 150 N. Describe the movement of the box. a The box begins to move as the applied force is larger than the friction force. d. Check the box that says, “Sum of Forces”. Repeat procedures a, b, and c. What was different about c? a The friction force was less than the applied force thus increasing the sum of forces. Summary Newton’s Second Law states “The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.” Explain how your observations relate to the underlined portion of this Law (hint, you might want to look up the definition of the word “net”). The net force can be split up into two components: horizontal and vertical. The net force is the sum of all the forces in the horizontal or vertical direction. When the box is not moving, the sum of the friction and applied force is zero, so the net force is zero. When the box is moving, the sum of the friction and applied force is greater than zero, so the net force is greater than zero.

Breana Aguilar PHY-10-0752 30 September 2023 Part V: Friction in Detail a. Reset the app. Check the force and speed box. Apply 50 N of force to the crate. Slowly click (in 50 N increments) to increase the amount of applied force until the crate starts to move/accelerate. Note the range of force values when the crate first started to move. Record this range below (e.g., starts moving somewhere between 0 and 50 N). a Starts moving at around 126-150 N. b. Reset the app. Repeat the steps in “a”. Once you have just made the crate move do not adjust the force any higher. Allow the block to move with this constant force for 2.0 seconds. Now reduce the force by 50 N. How does the crate behave immediately after reducing the force by 50 N? Did it keep accelerating? Move at a constant speed or decelerate? Does this behavior surprise you based on your knowledge of Newton’s 1 st and 2 nd Law. Why do you think the crate behaves this way? a The box slowly begins to decelerate, which is not surprising because the friction force is the only force acting in the horizontal direction which slows it down. c. Reset the app. Check the speed, force, sum of forces and values boxes. Adjust the value of the applied force using single Newton increments to determine the exact force required to make the crate move. Mentally note the value of this force so you can record it after in the space below. Now keep increasing the value of the applied force in large 50 N or small single Newton increments. What happens to size of the friction force? What is the value of the friction force now? Why does the friction force behave this way? It took 126 N to start pushing the box, and after increasing the force, the friction force (arrow) remained constant. There are two different friction forces, the static friction force, and the kinetic friction force. The static friction force is always larger than the kinetic friction force. This means that the box needs more force to overcome the static friction at first, then the kinetic friction is in play after the box starts to move. d. Repeat step c and after the block has accelerated for 3.0 seconds reduce the applied force to 0 N. What happens to the size of the friction force after the applied force goes to 0 N? How does the crate behave? a The friction force stays the same until the box stops moving, to which then it disappears. e. Reset the app. Check the forces, values, and speed boxes. Place another crate on top of the first. Determine the minimum amount of force required to move the crates. Determine the minimum amount of force required to keep the blocks moving at a constant speed. Record these below: a Minimum force required to move the crates: 251 N.

Breana Aguilar PHY-10-0752 30 September 2023 b Minimum amount of force required to keep the blocks moving at a constant speed: 188 N. i. How do these values compare to the values found for one crate? What does this tell you about the effect of mass on friction? a. The force required to move the crates is about double that of a single crate. Mass and friction are directly related, the larger the mass, the more friction is experienced. f. Reset the app. Check the force and values boxes. Apply 50 N of force to the crate. What is the value of the force of friction now? Record this. Increase the applied force and note how the friction force behaves. Record this behavior in the space below. a Force of friction is 50 N. b The force of friction increases to 125 N, to which then the box starts moving and the force of friction drops to 94 N. Summary Make four or more general statements about the force of friction based on your observations in parts a – f. The force of friction balances with applied force to a certain point. Once the box starts moving, the friction force decreases. The friction force is directly proportional to mass. The different surfaces have different amounts of friction.

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