Procedure Question:

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

Questions:

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

Draw a free body diagram of your box of water from the situation in Procedure 4d. Draw arrows for the force of gravity, the normal force (your hand pushing up on the box), and the stopping force (your hand decelerating the box as you stop.) What is the direction of the water’s acceleration?

*Note, free body diagrams are discussed in depth in Lab 2: Types of Forces. See Figure 3 for a sample diagram. Remember, the object is usually indicated as a box, and each force that acts upon the box is indicated with an arrow. The size of the arrow indicates the magnitude of the force, and the direction of the arrow indicates the direction which the force is acting. Each arrow should be labeled to identify the type of force. Note, not all objects have four forces acting upon them.

Ffriction

Fapp

Fnormal

Fgravity

Figure 3

Figure 3: Sample FBD

Can you think of an instance when you are driving or riding in a car that is similar to this experiment? Describe two instances where you feel forces in a car in terms of inertia.

Experiment 2: Unbalanced Forces – Newton’s Second Law

Table 1: Motion Data for Experiment 2

Trial

M1

M2

d of M2

Time (s)

Calculated Acceleration

Procedure 1

1

2

3

4

5

Average

Procedure 2

1

2

3

4

5

Average

Questions:

When you give one set of washers a downward push, does it move as easily as the other set? Does it stop before it reaches the floor? How do you explain this behavior?

Draw a FBD for M1 and M2 in each procedure (Procedure 1 and Procedure 2). Draw force arrows for the force due to gravity acting on both masses (Fg1 and Fg2), and the force of tension (FT). Also draw arrows indication the direction of acceleration, a.

Experiment 3: Newton’s Third Law

Questions:

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

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

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?

If the recoil of the rifle has the same magnitude force on the shooter as the rifle has on the bullet, why does the shooter not fly backwards with a high velocity?