# PHYS310 Lab 7 Newton's Law

*Tutorial includes complete laboratory (including methods and materials, experimental data, full explanations, and diagrams) with the following questions answered:*

Experiment 1: Newton’s First Law

4. Record your observations for each type of motion from Step 4 in the space below. Comment on where the water tended to move. If it spilled, note which side it spilled from.

Questions

1. Explain how your observations of the water demonstrate Newton’s law of inertia.

2. Draw free body diagrams for the box of water from the situation in Procedure 4d. Draw arrows for all forces exerted on the box—this will include the force of gravity, the normal force (exerted by your hands), and the stopping force (also exerted by your hands). What is the direction of the acceleration of the box?

3. Describe two situations where you feel forces in a car in a particular direction. Explain these forces in terms of the car’s acceleration and your body’s inertia.

Experiment 2: Unbalanced Forces-Newton’s Second Law

Table 1: Motion Data

Trial Number Time (s) Trial Number Time (s)

1 6

2 7

3 8

4 9

5 10

Average Time:

Calculations

1. Find the average acceleration of the washers using the average time above and the measured distance (half the total string length) using the kinematics equations:

Questions

1. Which example(s) represent balanced forces acting on the objects? Which example(s) demonstrate unbalanced forces?

2. Draw a FBD for both sets of washers when you had 5 suspended on each side. Calculate and label the magnitude of all forces, taking the mass of each washer to be 3.5 g. Label the tension force from the string T (what direction does this always point?).

3. Write out Newton’s second law fore each mass depicted in your FBD. Calculate the acceleration of each mass and the tension (T) of the string.

4. Draw similar diagrams for the cases where the mass is uneven, again labeling all forces. Use m1 = 5 washers and m2 = 10 washers.

5. Write out a second law equation for each mass in this uneven case. Why must the accelerations be equal?

6. Combine the above equations to solve for the overall acceleration of both masses and the string tension (T).

7. Use this equation to find the acceleration for the washers in Procedure 2 (6 and 5 washers). Why can you use the arbitrary mass units of 6 washers and 5 washers instead of grams or kilograms and still calculate an acceleration in m/s2?

8. Are your results in accordance with your prior calculation? Find the percent error between your calculated (theoretical) and measured (actual) values.

Experiment 3: Action/Reaction Pairs

Questions

1. Describe the motion of the balloon and the container once the pressure became too great.

2. If you conducted this experiment in outer space, how would the test tube and balloon move?

3. Calculate the accelerations for a 10 g balloon and a 5 g test tube if the force of the chemical reaction is 0.05 N. What would the velocity of each object be if the reaction exerted this force for 2 seconds?

4. Explain what causes the recoil of a powerful rifle or cannon when a projectile is fired at high speeds. Calculate the force required to accelerate a 30 g bullet to a speed of 400 m/s in 0.0025 s.

Experiment 4: Accelerating Balloon

Questions

1. Explain what caused the balloon to move in terms of Newton’s Third Law.

2. What is the force pair in this experiment? Draw a Free Body Diagram (FBD) to represent the (unbalanced) forces on the balloon/straw combination.

3. Add some mass to the straw by taping some metal washers to the bottom and repeat the experiment. How does this change the motion of the assembly? How does this change the FBD?

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