Kinetic and Potential Energy

Transcription

1 Kinetic and Potential Energy Objective: Prove or Disprove Galileo Free Falling Body Experiment Determine the energies involved of a free falling body Combine Kinetic and Gravitational Potential energy equation to solve complex problems. Introduce Period and Angular Momentum for measurement of a Pendulum. Purpose: Understanding energy is the key to physics and the universe around us. It does not matter what course work anyone studies there is always a component of energy. This lab will introduce two aspects of energy and how to solve some complex problems with just calculating the energy involved. Aristotle was approached with a question of which will fall faster between two rocks. After pondering the question for a period of time, he concluded that the heavier object would fall at a faster rate. Galileo challenged this concept about 2000 years later. In a previous lab we discuss the Free Falling body experiment. We saw in the experiment that object will fall at the same rate with a different mass as long as the volume is the same for each object; therefore mass is not relevant in a free falling body.

2 Newton was the next person to approach this problem using his equations of motion, mainly the Universal Gravitation equation. Though this equation is good for measuring the force, but in order to have any force there must be energy transferred from one place to another. Kinetic Energy is a very versatile equation to figure out how much energy a moving object has. The term Kinetic means an object in motion. A Static object is one that is at rest (not moving). The above equation is used to solve the Kinetic Energy of an object. The m is the mass of the object and v is the velocity of the object in motion. This raises the question of how is mass irrelevant as explained above? If you are solely looking at the kinetic energy of a moving object such as a car; then the mass is very important. As we saw in the previous lab this equation can solve for the change in kinetic energy you can figure out the work done. We will use kinetic energy in another facet in this lab. There is another way in order to determine the change in kinetic energy by looking a new concept called Gravitation Potential Energy. Here m is still the mass, g is gravity (not to be associated with the acceleration due to gravity because g is a scalar) and h is the maximum height of the object of your reference frame. As the name suggests this is going to be the energy stored in the object while at rest. At rest the GPE will be a maximum. As the object moves towards the center of the gravitation force the GPE will start to decrease. What happens to the energy if the GPE is decreasing? There is a Law dealing with changing of energy and how it works in the universe. This law is called the Conservation of Energy. Law of Conservation of Energy Within some problem domain, the amount of energy remains constant and energy is neither created nor destroyed. Energy can be converted from one form to another (potential energy can be converted to kinetic energy) but the total energy within the domain remains fixed. (Glen Research Center NASA) \

3 Here we can see that the energy will be the same, to see how this works you will add all the energies of the system together. In this experiment we will prove the conservation of energy using kinetic energy and gravitational potential energy. This is known as a conservative concept. When the energies or forces do not remain fixed in a system then this will be called a nonconservative concept. Conservation of change in kinetic energy In our last lab we saw that a change in kinetic energy will also solve for the work done by or on a system. This is another way to solve the same problems as in the last lab. Try repeating some of the questions from the last lab using the conservation of change in kinetic energy and see if you still get the same results. Materials: (1) Pasco Scientific Projectile Launcher (ME-6800) (1) Pasco Scientific Drop Shoot Accessory (ME-9859) (1) Pasco Scientific Time of Flight Accessory (1) Pasco Scientific PhotoGate with interface cord (2) Steel ball (65g) (1) Steel ball (25g) Procedure: Part I (1) Gather all necessary equipment to complete this lab (2) Attach the Drop Shoot Accessory to the Projectile launcher by sliding the nut on the accessory into the bottom slide of the projectile launcher. (3) Make sure the accessory is flush with the barrel of the launcher and tighten the nut on to secure the accessory in place. (4) Unscrew the retaining nut on the steel bolt. (5) Place the opening on the back of the photogate onto the steel screw (6) Replace the retaining nut to secure the photogate in place. (7) Plug in the telephonic connector into the back of the photogate. (8) Plug the RCA connector of the photogate into channel 1 on the interface.

4 (9) Plug the RCA connector on the Time of Flight accessory into channel 2 on the interface (10) Place the Time of Flight accessory underneath the Drop Shoot Accessory as show in the picture. (11) Open the file KE GPE in the capstone folder on your desk top. (12) Use the plum bob on the launcher to make sure the bob is resting at 0⁰ for this entire experiment. *Note* the angle will shift after repeated launches, it is important to check the angle after every launch. (13) Using two balls of the same mass (use scale if needed to check, a 10% variance is acceptable) (14) Load one steel ball into the launcher at the setting SHORT RANGE (15) Attached the other steel ball to the base of the black bolt. *NOTE* the base of the black bolt is magnetic and will hold the ball in place. (16) Using the picture on the side of the launcher that explains the position of the ball inside the launcher, Adjust the height of the black bolt so that both balls are at the same height. (17) Click the button in capstone (18) Pull up in the yellow string to fire the launcher

5 (19) Click in capstone. (20) Repeat steps for a total of 5 (five) runs (run#1-5). Collect data for FREE FALL *NOTE* Not all five runs will be displayed at the same time, we will correct this later. (21) Move the time of flight accessory to gather the data for the PROJECTILE MOTION ball. (22) Adjust the distance with test launches before (Recording) any data. (23) Repeat steps for a total of 5 (five) runs (run#6-10). (24) In the table you will see that all fields have the same RUN # (25) Left Click each field and a drop down menu shows you all the RUN # s. (26) Starting on the far left assign each field its corresponding run, start with RUN 1, RUN2, and RUN3 and so on until you have reach TEN runs. (27) This is the complete table of times of flight for two objects of the same masses. (28) Print this table. (29) Select the UNEQUAL MASSES tab in capstone. (30) Replace one steel ball for the lighter mass steel ball (hollow) (31) The larger mass ball will be the only ball loaded into the launcher (32) The hollow steel ball will be attached to the magnet (33) Repeat steps with RUN #s (run# 11-15) for free fall and (run # 16-20) for projectile time. (34) Print both sets of tables. Part II (35) Select the higher mass ball and insert the ball into the Pendulum. There is a locking device so the ball will not leave the Pendulum randomly. (36) Gently remove the screw holding the pendulum to the stand. (37) Measure the complete mass of the Pendulum, ball, and masses attached. This will be your mass for your equation (38) Record the mass in the Excel workbook (39) Measure the length of the pendulum from top to the center of the ball. (40) Record the length in the Excel workbook (41) Record gravity in the Excel workbook

6 Questions: (42) Replace the pendulum by inserting the bolt removed and gently tighten the pendulum in place. DO NOT OVER TIGHTEN THE BOLT! (43) The angle indicator will tell you the angle in which the max height is reached. At rest the angle indicator should be at zero. If there is a issue in which this is not the case, continue with the experiment and adjust your angle measurement to compensate for the error. (44) Pull back on the pendulum (45) Release the pendulum with the objective of getting close to 10⁰. This does not need to be exactly 10⁰ but just close. (46) Record the angle on the angle indicator in the Excel work book. (47) Repeat steps (43-45) for angles Remember this does not need to be exact to the angle, but it does need to be close.(within 5⁰) (48) Repeat Steps (44-47) for the lighter mass ball. (49) Print Excel Graphs. (1) What is the importance of the free fall experiment? (2) Though the mass is not important will the Potential Energy and Kinetic Energy change with the free fall experiment? (3) You drop a ball from the roof of the library with a mass of.20kg at height of 30m; what is the velocity of the ball at impact with the ground? (4) What is the Potential and kinetic energy half way through the free fall in question (3)? (5) At what point is the Potential Energy at a maximum? (6) At what point is the Kinetic Energy at a maximum?