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Ballistic_Pendulum_Instructions

# Ballistic_Pendulum_Instructions - instructions for Use of...

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Unformatted text preview: instructions for Use of M0870 Ballistics Pendulum Conservation of Momentun Purpose: This experiment demonstrates the conservation of momentum during a collision. and distinguishes between the conservation of total energy and the conservation of mechanical energy. introduction: A spring "gun" hurls a sphere in a horizontal trajectory so that it hits a catcher mounted on a rod attached to a pivot. This apparatus is called a ballistic pendulum. The catcher traps the sphere in an inelastic collision so that its momentum may be conserved. The catcher plus sphere then has a velocity that makes thorn rotate in a vertical plane about the pivot until the potential energy becomes equal to that of the kinetic energy after the cotlsion. The pivot has a built-in clutch that holds the pendulum at its highest point and allows an easy measurement at the potential energy irioresse. While the Mechanical energy (kinetic plus potential] after the collision is conserved. the mechanical energy during the collision is not conserved. A test at these theoretical principles 1rlrill be made by performing two related experiments and comparing the results. The ﬁrst experiment measures the increase in potential energy of both the catcher and the sphere as a result of the collision. and uses the conservation cf'energy and momentum to determine the Initial velocity of the sphere just beiore it strikes the catcher. The second experiment independently finds the Initial velocity of the sphere by melting a kinematic measurement of the horizontal distance traveled for a partlmlar vertical height when the sphere acts as a projectile. ll Namonian theory is correct. these two Initial velocities should agree within expenmentai error. Equipment Required: A Sargent¥welch WLOBS'O Ballistic Pendulum. meter stick. can balance [100 g capacity), C-clamp (optional). smooth hard surface {clipboard}. and carbon paper. -2- 3. Position the assembled ballistics plﬂdulum at the edge of e table or let: sol-tori. Turn the feet up or dorm on the bottom of the base until the bubble in the level. located near the ppm. Indicates that the pendulum hose is perfectly level. Clamp the bees to the tabletop to prevent accidental movement. CAUTION: ﬂee care when opererttng this entice. Do not stem! or place trends or body in the peth oi the projectile. at. AdJUHment of the sphere. velocity can be mede by turning the sleeve on the horizontal shah which is located on the end of the trigger assembly furthest from the pendulum peat mambly. Rotation of the sleeve oneness the tension on the spring inside the trigger assembly and produces e mtfoeeble effect only after several complete turns. it is easier to tum the edictstment sleeve before the trigger assembly is in the 'oocited" position. The adjustment sleeve should not be changed until both peril of the etcpuerirnent are completed. Pendulum Experiment t. . Introduction: In title first of hvc experiments to ﬁnd the initial velocity of the sphere. the sphere will be projected Into the catcher and cause them both to rotete ebout the pivot. The sphere of mass m has a velocity v immediately before it reaches the catcher. The sphere then collides ineteattceliy with the catcher {nines M} to give the combined messes a horizontal veiodty v. During the collision. momentum is conserved. but niechanfcat energy {the sum of kinetic and potential] Is not. Momentum ts omserved because no enamel {horizontal} forces act on the system. Mechanic! energy is not conserved becetrse the collision is inelastic. “thus. the kinetic energy of the sphere before the collision will not be equal to the potential energy of the sphere end catcher at their highest point after the collision. Hort-rover. the kinetic energy of the sphere end catcher immediately after the collision vrill be equal to their potential energy et the highest point of their arc. F3_ Procedure: The mass m of the sphere should be determined on a pan balance. [The steel sphere has an approximate mass of Ed g}. The effective mass of the catcher {11B 9] appears on the rear of the tripoer housing assembly since the catcher cannot be removed and mounted separately. The center at the mess of the catcherisphere appears as a red dot on the catcher. The difference bemoan the height of this dot before and after the sphere is protected into the catcher is the increase In height h in the equations above. To use the ballistic pendulum most effectively. proceed as follows: 1. 5. Be sure that the assembly instructions at the beginning of this description have been. followed carefully. To fire the sphere. side the sphere onto the horizontal rod projecting toward the penicillin poet assenbly and its catcher. Be sure the sphere is flnnly seated. The firing mechanism is srrried men the where and red are pusriao horizornally away from the catcher until the trigger engages. csurton: the care when operating this device. he not stand or piece hands or body In the path of the projectile once the mechanism is armed. After the mechanism is armed. loosen the knob on top of the post so that the pendulum can swing freely. Push the alignment pin {the small red with red plastic ends] to the rear. Do not let the pendulum and sphere strike the horizontal red when resetting as this may deform the rod end. IMPOHTMT: If comistentiy aowrate readings are to be made. the heart instruction must be followed exactly. With the top knob loose. guide the pendulum until it touches the sphere. Hold it there while tightening the lrnoh on the top of the post. After the lrnob Is tightened. 'out before letting the pendulum go. britg the alignment pin to the front. Then let the continuum swing gently bars: until it touches the alignment pin. At that point. gently pull the pln to the rear. This operation exactly aligns the pendulum in the vertical position and reduces backlash in the roller clumh. Measure the vertical distance from the base to the red dot on the catcher. Fire the pendulum by tapping down on the trigger lever located directly above 1le sphere. The sphere will be propelled forward to hit the pendulum catcher. becoming hopped in the rubber wedges and causing the pendulum to are upwards. The roller clutch all stop the pendulum at the peak of its arc and prevent it from dropping back down to its starting cushion. Determine the Wrﬂﬁll defence from the base to the red dot on the catcher. The difference between this diatoms and that measured in step 5 is the height it. Repeat steps 2 through I about ten times and use an average value for the height h. After measuring. loosen the knob and let the pendJIum slowly return to the starting position. GAUTIOH: Do not let the sphere and catcher strike the horizontal rod. To do so may cause deformation of the rod. find the initial velocity of the sphere before it hits the catcher. This is a value determined by assuming tliet momentum is conserved during the collision and mechanical energy is conserved after the collision. This VINE of y will be determined independently as deserted in the nest experiment. -4- Projectile Motion This is a purely kinematic expert-cent to determine the initial velocity oi the sphere. The sphere will be protected horizontally and the horizontal distance it travels before striking the ﬂoor will be measured along with the ephere's initial vertical height above the floor. The sphere travels in a parabolic arc with a commit horizontal velocity and a constant vertical acceleration. The sphere is In the air for a time t timing which it travels a horizontal distance R The values of Ft and H can be measured by the followhp procedure. 1. The ballistic pendulum would be set up at the one or a table as described at the beginning of this guide. The tension edjimtrnent should not be changed between the previous experiment and this one. 2. Ftotete the catcher awayr from the trigger assembly until it is parallel to the tabletop and out oi the launcl‘ler'e line of fire. Tighten the knob on the top of the pendulum assembly so the catcher stays out of the way. -5- Fire the sphere out onto the floor to dieternine approximately where it will fall. Position a smooth hard surface [such as a clipboard] at the point where the sphere hits the floor. Tape a piece of paper to the board's surface with a piece of carbon paper on top of it and tape the board to the ﬂoor to prevent rnovement. Place a protective piece of paper over the carbon paper to keep it from testing. The sphere will strike the target and the carbon paper will leave a mark on the paper beneath it. Fire the sphere onto the target ten times. CAUTION: Use care when operating this device. Do not stand or place hands or body In the path at the prelectl'le once the mechanism It armed. Measure the horizontal distance from the and of the firing pin to each merit. The average of these distances is H. measure the vertical distance from the bottom of the sphere to the floor when it is on its red {hm not when the firing mechanism is cooked}. Subtract the thickness of the target to determine the vertical distance H. The velocity v at the sphere can now be calculated and compared with the value found in the ﬁrst experiment. You would expect the two values to agree within the accuracy of your measurements. If they do. you have confirmed the Iainr of conservation of momenttml Questions: 1. In addition to the measured errors in the parameters h In the first experiment and R in the second. a number of assumptions were also made in the equations. The first experiment neglected the friction in the ruler hearings and slippage of the clutch: the second experiment neglected air friction. ‘t‘ou can think of other smurnptlons. Make a list and describe how each would effect the calculated values of v. Earlier It was stated that mechanical energyI was not conserved during the coaision. Verify thls by calculating the velocity V of the sphere and catcher after the collision. and then determining the kinetic energy tetm + MW! of this combination. Compare that energy with the kinetic energy of the sphere is mv2 before the collision. Even though these two energies are quite dilterent. the total energy of the system was conserved. The difference in kinetic energies went into than-nal energy that warmed the sphere and catcher. ...
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Ballistic_Pendulum_Instructions - instructions for Use of...

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