# ACTIVITY #2: Knock‘em Down

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ACTIVITY #2: Knock‘em Down
Bowling is a good example of an instance where we take advantage of the speed of an object, in this case the bowling ball. The idea is to give the ball enough speed so that it can knock down the pins it comes in contact with, and then those pins will bounce around and strike other pins. Why does the speed of the ball play an important role in determining how many pins will be knocked down? Would it matter if the bowling ball were hollow?

GOALS: In this lab activity, you will …
·        Determine how the speed of an object will influence the amount of change that it can produce. ·        Determine how the mass of an object will influence the amount of change that it can produce. ·        Establish a connection between the mass and speed of an object, and its energy of motion (kinetic energy). MAIN IDEAS: The important concepts and skills covered in this activity are … ·        A moving object has energy because of its motion. This energy, called kinetic energy, gives us an indication of how much a moving object can change the motion of other objects. ·        The kinetic energy of an object is determined by its speed and mass. Increasing the size of the speed and/or the mass increases the object’s kinetic energy. ·        Energy Transfer takes place whenever energy is ‘passed’ from one object to another object.

Activity Overview: A synopsis of this lesson is as follows…
A ball is released from the top of a ramp. It rolls down the ramp onto a horizontal surface. There are obstructions (index cards taped to the table) on the level surface in the path of the ball. The ball collides with these obstructions, knocking them over. The height of the ramp is then increased and the exercise repeated. In the previous activity, it was established that increasing the height of the ramp increases the ball’s speed at the bottom of the ramp. In the first part of this activity, we investigate how the speed of a moving ball affects its ability to change the motion of other objects. The ball will then be replaced with a ball of similar size, but smaller mass, and the activity will be repeated. Once it is established that both the mass and the speed of an object influence its effect on other objects, the combined effect of the mass and speed of an object are defined to be its ‘energy of motion’, called the kinetic energy.

MAKING SENSE OF ENERGY …
Energy is the most central concept in all of science. It is the thread that ties the physical, life, and earth sciences together. Matter and energy make up the universe. We commonly say that objects have energy, but we can’t really see this energy. We recognize energy mainly through the effects it has on objects. We see things happen and changes occur when an object or substance has energy and shares that energy with other objects. Scientists long ago noticed patterns emerging through their experiments. One story suggests that Galileo watched a pendulum in a clock rock back-and-forth during a church sermon. He wondered why the pendulum kept swinging without slowing down much and how the pendulum could stop at the ends of the swing, yet speed up while approaching the center of the swing. He questioned if there something being saved up during each swing. These types of observations were repeated by other scientists that followed Galileo. Sir Isaac Newton used the conclusions of Galileo to formulate his famous three laws of motion, but ironically, Newton’s work included nothing about energy. It appears that the famous Isaac Newton was not aware of energy. The concept of energy was not developed and used to explain physical changes until the 1800’s, more than a hundred years after Newton’s death. Today, the concept of energy is a key idea in all the sciences.

Energy is not easily defined, so historically, scientists studied energy by looking at the effects it had on matter. A loose definition that is sometimes used for energy is “the ability to bring about some sort of change.” In other words, if something has energy, then it can cause a change in itself or its surroundings. By designing experiments to study these changes, scientists learn more about energy.

Let’s Investigate … PART A - The Energy of Motion of a Solid Golf Ball Gather the materials needed to replicate the experimental setup from the previous investigation. We will use the average speed results from the Balls & Ramps activity in this lesson. Cut about 6 index cards (3 inch x 5 inch) in half across the short size of the card (figure #1). Then make a fold on each such that the card is divided into a 1/3 section and a 2/3 section (figure #2). The 1/3 section will get taped to the table. (2cm and 4 cm)

You will find it convenient to tape the base of each card to the table top and use two meter sticks to serve as guides on either side of the row of cards as shown in the figures. 3.Setup the index cards in a straight line starting at a distance of 10 cm from the bottom of the ramp. Space each card about 5 cm apart. 4.Release the solid ball from the top of the ramp and record the number of cards that the ball knocks over. If the cards are numbered from 0 to 11, then the number written on the card that the ball land on is also the number of cards knocked over by the ball

5. Repeat the task 4 more times at that release height
5.Repeat the task 4 more times at that release height. Determine the average number of cards knocked over by the ball for that release height. 6.Record your result in the data table along with the speed of the ball for this release height. (This speed was calculated and recorded in Activity 1.) 7.Increase the height of the ramp by adding another wooden block and then repeat steps #4, 5, & 6 if this experiment. 8.Use your results and graph the Number of Cards (knocked down) versus the Speed of the Ball for the solid golf ball. Be sure to label your axes and provide a title.

Question #1: As the release height of the golf ball is increased, how does the speed of the ball at the bottom of the ramp change? Question #2: Based on your graph, what effect does the speed of the golf ball have on the number of cards it knocks down?

PART B - The Energy of Motion of a Hollow Golf Ball
In Part B the solid golf ball will be replaced by a hollow plastic golf ball, and the experiment you just completed in Part A will be repeated. Question #3: By replacing a solid golf ball with a hollow golf ball and repeating the experiment of Part A, what variables will be changed, and what variables will be kept the same? Replace the solid golf ball with a hollow “practice” golf ball and repeat steps #4 to #7 in Part A of this experiment. Use your results and graph the Number of Cards (knocked down) versus the Speed of the Ball for the hollow golf ball on the same set of axes used in Part A.

Question #4: What effect did changing the mass of the ball (substituting the hollow ball for the solid ball) have on the resulting number of cards knocked down? MAKING SENSE OF ENERGY … In Activity 1, we determined that as the release height of a golf ball increases, so does its speed. In this activity, we found that as the object’s speed increase, so does its ability to create change. The “change” in this activity is the knocking down of index cards. We also found that the mass of the golf ball plays an important role in determining how much change it can produce. The ability of a moving object to cause change is important and we have found that both the speed and mass determine this ability.

In science, we define a quantity that describes how much change an object can produce as its ‘energy of motion’, more commonly called the kinetic energy Through our experiments, we found that the kinetic energy of the golf balls depends upon the speed and mass of the balls. What is true for golf balls is also true for other objects. Every moving object; cars, trains, planes, soccer balls, basketball players, ballerinas, river water, even clouds has kinetic energy. If the object has mass and is moving, it has kinetic energy. Your experiments indicate that as the speed and/or mass of the object increases, its kinetic energy increases too. Additional questions to ponder … Question: Look at the results of your experiments and identify in which case the golf ball had the greatest kinetic energy. Question: Considering the entire motion of the golf ball, from its release at the top of the ramp to the point where it comes to rest. At what point in its motion does the ball have its greatest kinetic energy? Question: In the question above, you identified the solid golf ball as having the greatest kinetic energy. Describe how you could give the hollow golf ball this same amount of kinetic energy.

In your journal or notebook, write a concise summary of this activity.
Summary of Activity … In your journal or notebook, write a concise summary of this activity. Be sure to address the following questions and use your data to support your responses. What was the “change” produced by the ball? In this activity, what factors determine the kinetic energy (KE) of the ball?