LAB V: ACCELERATION

Problem: What is the relationship between the distance an accelerating object travels and the time it takes to travel that distance?

NOTE: DO NOT BEGIN YOUR EXPERIMENT UNTIL EACH PERSON IN YOUR GROUP HAS READ THE BACKGROUND AND COMPLETED THE BACKGROUND QUESTIONS.

Background and Inquiry: Why will a penny dropped off the Empire State Building become a deadly object? It is because objects in free-fall accelerate. The further they drop the faster they travel. By the time the penny reaches the ground it will be traveling faster than a racing car. Galileo was the first scientist to prove that all objects fall at the same acceleration. We will notice a difference however if we drop a piece of paper. The paper has a different acceleration because of air pressure and frictional forces.

It is difficult to study the motion of falling objects because they are moving too rapidly. Take each of the balls (handball and Ping-Pong ball). Drop them from a feet high. Can you observe any changes in velocity? Drop the balls from a height of only one foot. Drop the balls from different heights and observe and discuss with your group what you observe.

By using an inclined plane we may slow the movement of accelerating objects. Today you will study acceleration in an experiment by rolling a ball down an incline plane. Acceleration is defined as a change in velocity. Velocity is defined as a change in distance per unit of time. Acceleration occurs because a force is applied to an object. As long as the force is applied the object will accelerate. In the case of falling objects the force applied is gravity. As the ball begins to move under the force of gravity it will accelerate. The further the ball goes the faster it will travel.

Background Questions:

1) What is velocity?
2) What is acceleration? How is acceleration different from velocity?
3) What are some conditions that will change the acceleration of the rolling objects?
4) If a rock and a feather are dropped on the moon why do they fall at the same rate while on earth they do not?
5) Would friction or air pressure affect how fast a ball rolls down a incline? Why?

Hypothesis: State your hypothesis. Justify your statement!

Materials: Inclined plane, two meter sticks, ping pong ball, handball, golf ball, 2 digital watch timer.

Diagram: Include a diagram in you lab report.

Procedure:
1) Copy Table I , Table II, Table III.
2) Set up the equipment as shown in in class.
3) Set the incline plane for 35 degrees. You will record the time it takes the ball to roll down the incline every 20 cm. There should already be 20 cm. marks on the incline.
4) Start with the ping pong ball. Let the ball start rolling from 0 cm. Start your timer.
5) When the ball reaches the 20 cm. stop your timer. Let the ball roll off the incline.
6) Record your time in Table I (see results section). Repeat a second time. Then average the two times.
7) Repeat the process and record the time it takes till the ball reaches the 40 cm. mark, 60 cm. Mark etc....

8)Record your data in Table I.

9) Set the incline for 40 degrees and complete Table II.
10) Repeat steps 5-9 using the handball instead of the ping pong ball.

TABLE I --Incline set at 35 degrees -- ping pong ball

TABLE II Incline set at 35 degrees -- Blue Handball

PART II:

In this experiment you will study the effect that changing the angle of the incline will have on the force of a rolling golf ball. Remember that Newton's Second Law of motion states that F = ma (Force = mass x accleration). Does this mean that if an object has a greater acceleration it can apply a greater force?

1) For table III below you will change the angle of the incline.

2) Set the paper cup at the end of the incline so the golf ball will roll into the cup.

3) Roll the golf ball from the top of the incline and measure how far the cup travels. It does not matter what part of the cup you use for your measurements as long a you always use the same part in your calculation.

TABLE III --

Graphing:
1) Make plots for Table I and Table II on the same graph. Plot time on the y-axis and distance on the x-axis.
2) Make a graph of Table ^{III, plotting the angle of incline on the x-axis and the distance the cup moves on the y-axis.}

Discussion:

1) What are the independent and dependent variables for table I and II?
2) What are the independent and dependent variables for table III?
3) What are some factors held constant in each experiment?
4) What type of relationship is observed for your graphs in table I and table II, linear or non-linear? Why is this the case?
5) If all objects accelerate at the same rate explain your differences between the handball and ping pong ball.
6) Why did increasing the angle of the incline in Table III cause the cup to move further away?
7) What type of relationship is observed for table III. Why do you think this is the case?

Applications: Design an experiment to determine the rate of acceleration of a falling object.