Lab report 4 - Newton\'s Law PDF

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Lab report for physics 110 lab. About Newton’s Law...

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Physics 110 Section 8 Lab Assignment #4 Newton’s Laws and Forces in 1 Dimension 3/22/2021 Jasmine Chim

Introduction: Newton has three laws of motion that describes how an object is moved and affected by external forces. His first law says that an object will remain at rest and at constant motion unless a force is acted upon it. His second law states that multiple forces act on an object and that the sum of these forces is equal to the mass of the object times to its acceleration. Usually when an object is falling, the acceleration would be the earth’s gravity. His third and final law states that a force exerted on an object will exert back the same force. The net acceleration of the two forces added together is zero. The opposing force is called the normal force and that is perpendicular the slope of the object. Friction is a kind of normal force that acts against the motion of the object. The friction force is opposite tot eh direction of the applied direction of motion. There are two kinds of friction force: Static friction and kinetic friction. Static friction is the force that is capable of keeping an object from moving. Once the applied force multiplied by the static constant then the object will begin to more and the friction turns into kinetic friction. The force is between two objects moving against each other and it is less compared to static friction. Procedure: 1. Open the simulation and play around with the controls to see the relationship between force vs. time and how an objects mass affects the data. a. Do procedure question 2. In the simulation, apply 600N of force for 5 seconds to an object and then calculate the objects distance with there is no friction. 3. Slowly increased the applied force and then stop with the object begins to move. Find out what happened to the friction force and why. 4. Restart and continue to apply force after the object start moving. Calculate the coefficient of kinetic friction. 5. Repeat step 3 and 4 with another object on the list. 6. Try this experiment at home with a plastic object on a surface without water/oil then with water and another surface with oil. Observe how fast the object moves each time with a light tap. 7. In the next part of the experiment, open the inclined ramp simulation and describe the force of the cabinet when the angle of the ramp is 0. 8. Slowly life the cabinet by increasing the ramps angle and see how the force on the cabinet is changed. Record at what angle the cabinet begins to move. 9. Replace the cabinet now with a 300kg crate and repeat steps 7 and 8. Note any notable distances between the two. Pre-Lab: 1. Imagine you are in a car without a seat belt, travelling at a constant speed. Suddenly, you traffic light turns red, and you are forced to brake, and you find yourself lurching forward. Why is that so? - When you are sitting in a car and the car is in motion, you remain still because you are moving at the same speed as the car. For example, if the car was going 30 mph,

and you were sitting in it, then you were going at 30 mph as well. You remain still because you and the car are going at the same rate. When the car suddenly stops its speed is no longer 30 mph however you are still going at 30 mph. This is why you lurch forward. 2. A force F acts on a mass M, for some time interval T, giving it an initial speed v. If the same force acted on another mass 3M, what would be the initial speed of the new mass (in terms of v)? - V = [F x deltaT]/3m Results: Testing Static and Kinetic Friction Experiment - After applying 600N of force for 5 seconds, assuming there was no friction on the cabinet, they cabinet went 30.7 meters. -

o The friction force will increase in the opposite direction of the applied force for the same magnitude. The total force equals to 0N when the cabinet did not move (Newton’s third law). The reason why the total force changes so drastically is because the force of friction is changed from static to kinetic. The force of kinetic friction will apply less resistance than static so less force can be applied to and still the cabinet will still move.

o Fs = µ x FN

µ = Fs/FN  µ = Fs/(mg)  µ = 589/ (200 x 9.8)  µ = 0.3

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o The friction force remained constant at 392N. Depending on how much force is applied. A negative total force causes the cabinet to slow down until it eventually stops and the kinetic friction becomes static again. A positive total force will cause the cabinet to continue to move. At a constant applied force, the velocity will increase in small increments. o FK = µ x FN µ = FK/FN  µ = FK/(mg)  µ = 392/ (200 x 9.8)  µ = 0.2 Dog (25 kg) o Fs = µ x FN µ = Fs/FN  µ = Fs/(mg)  µ = 25/(25 x 9.8)  µ = 0.1 o FK = µ x FN µ = FK/FN  µ = FK/(mg)  µ = 24.5/(25 x 9.8)  µ = 0.1 o The coefficient is not the same to the cabinet because the dog has significantly less mass. The static friction would be less than the cabinet because of this. Ironically the static and kinetic frictions are the same for the dog however the data still shows the force of friction when the dog was stationary versus to when the dog is moving is still higher which further proves that static friction would require more force to overcome.

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The plastic object moves faster on a wet/oily surface because there is less friction. For drivers, driving on wet roads can cause accidents if there Is not enough friction for a car to stop or slow down.

Inclined Ramp - The force on the file cabinet is the gravitational force. That is the opposing force to the force of friction that is preventing the cabinet from falling down the ramp. When you slowly lift the ramp up the frictional force tries to match this until the object starts to move and the friction turns into kinetic. The only way the object would stop is if the ramp was lower or there was an applied force to stop or slow down the object from moving. On a horizontal plane the kinetic force of friction remained the same, but as seen in this experiment the force of friction changes as the object slides down the ramp. The force from the wall and the applied force is not changed. - The cabinet begins to fall at an angle of 17.2° - If you replace the cabinet with the crate, the angle at which the crate slides down the ramp is steeper and that means the object has more static friction to hold itself against the gravitational force. It starts to fall down the ramp at an angle of 35.4°. Post Lab Questions: 1. A 1200kg car is driving along a straight road at a speed of 50 m/s, when it brakes sharply. The resulting friction brings the car to rest. What is the frictional force if the coefficient of friction is 0.6, and how far does the car travel before it comes to rest?

2. A 12kg slab is being dragged across a dirt path with an applied force of 300N and has a net acceleration of 5m/s^2. What is the coefficient of static friction between the slab and the ground?

3. Imagine a 60 kg skydiver free-falling to earth, when they pull their parachute. After pulling the parachute, they descend 46 meters in 4 seconds. Draw a free body diagram labelling all the forces on the skydiver. The relative magnitudes of all forces should be drawn to scale. What is the force of air resistance on the diver?

4. A toddler exerts a horizontal force of 20 N to pull a mass of 50 kg on a horizontal surface whose coefficient of static friction is 0.1. Find the static friction force and explain how you obtain your answer.

5. A 10 kg mass is placed on an incline as shown. The coefficient of static friction is 0.5. Will this mass slide? Find the frictional force and explain how you obtain your answer.

Conclusion: In conclusion, Newton’s gravitational law can be seen in this experiment. His first law can be demonstrated when the no force was applied to the object. The object remained stationary. When the object received a constant amount of force (without friction) it moved a greater distance. His second law can be seen when we switched out the cabinet for a dog in the first part of the experiment and when we switched out the cabinet for the crate. It requires more force to move a heavier object than a light one. His third law of motion is proven when we try to apply force to an object. The force of friction equaled the force applied and that is why the object did not move. The simulation also shows how friction force changes from static to kinetic. Until the force applied is enough to overcome the force friction when the object is static, the applied force will equal the friction force. Once static friction force is overcoming it turns into kinetic and less force would be needed to keep the object in motion. The simulation also shows how ramp angle increased the effects of gravity and therefore made it easier to move the object. Less force is needed to apply to move the object due to the help of gravity....