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MECHANICS Introduction The lecture demonstrations listed in this section also include a short description and outline of how the demonstration experiment works. This is for the benefit of the lecturer (who is going to use it in the classroom) and the student (who will see it demonstrated in class). [To the lecturer: All of the equipment used in these demonstrations is stored in Heldenfels Hall. Some of the equipment is rather delicate and not easily transported to other buildings (our only mode of transport is a cart pushed by hand). When requesting a demonstration, be sure to mention the reference number and name listed in this section (example MEC-1 Friction). Requests for demonstrations to be set up in a different building from Heldenfels will require at least 3 class-days notice. The logistics of setting up demonstrations in different buildings gets difficult without advance notice. Practice with the apparatus prior to use in the classroom is always encouraged.] Contents MEC-01 Friction MEC-02 Acceleration on a Linear Track MEC-03 Feather and Coin in a Vacuum MEC-04 Inertia of Soda Cans MEC-05 Inertia of Mass on a String MEC-06 Drop and Shoot Apparatus MEC-07 Projectile Motion MEC-08 Loop the Loop MEC-09 Swinging Bowling Ball MEC-10 Whirling Beaker of Water MEC-11 Whirling Clothes Hanger and Coin MEC-12 Elastic & Inelastic Collisions on a Linear Track MEC-13 Newton’s Collision Balls MEC-14 Center of Gravity w/ Chalkboards

MEC-15 Center of Gravity with a Belt MEC-16 Moment of Inertia-Disc and Ring MEC-17 Conservation of Ang. Momemtum MEC-18 Spool and String MEC-19 Gryroscope MEC-20 Free Falling Hinged Board MEC-21 Simple Harmonic Motion MEC-22 Evacuated Can MEC-23 Cartesian Diver in a Bottle MEC-24 Geyser Effect MEC-25 Pascal’s Vases MEC-26 Archimedes’ Principle MEC-27 Constant Level Tubes MEC-28 Bernoulli’s Principle

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MEC-1 FRICTION Equipment: wood board (1ft x 3ft, with sandpaper strip on one side) 20N spring scale wood block (w/string attached) aluminum block (w/string attached) wood spacers (used to elevate board) Comments: Use the spring scale to pull on the blocks (with the board level on the table or elevated with the supports). Show the variation of friction of the two blocks. The wood board may also be raised at one end until the block slides.

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MEC-2 ACCELERATION ON A LINEAR TRACK Equipment: Pasco Linear Track Pasco cart 1 black metal block Wood spacers (2 ea, to elevate the track) Comments: The cart may be used to show acceleration when placed on the track (elevated with the spacers at one end). The cart may also be loaded with the black metal block (which is the about the same mass as the cart). DO NOT ALLOW THE CART TO FALL ON THE FLOOR.

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MEC-3 FEATHER AND COIN IN A VACUUM Equipment: Vacuum pump and hose Lucite tube Feather and plastic device (coin substitute) Comments: Compare how the two objects fall in the tube without a vacuum. Connect the vacuum pump and evacuate the lucite tube. Compare how the two objects fall in a vacuum.

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MEC-4 INERTIA OF SODA CANS

Stack 4 or 5 soda cans, one on top of another, on the cloth supplied. Make sure the bottom can is not wet or sticky with leftover soda. Pull the cloth quickly, on a line even with the table top. [Equipment: 4 or 5 soda cans Small piece of cloth]

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MEC-5 INERTIA OF A MASS Equipment: A frame consisting of a table clamp with a long ¾ inch OD steel rod

attached vertically and a two-way clamp with a short steel rod extending to one side.

Steel ball (about 8 cm diameter, with 2 eyehooks) Cardboard box with foam inside (to catch steel ball) Short steel rod Ball of light-weight string Comments: Attach the steel ball to the top cross member of the frame with a short loop of string. Tie another loop of string on the bottom of the steel ball. Place the short metal rod through the loop of string at the bottom of the steel ball and show that a steady downward pull on the rod will break the top string. Retie the loop at the top and then show that a quick downward pull on the rod will break the bottom string. The loops should be about 6 inch diameter. Be sure that the cardboard box is under the steel ball (to prevent it from hitting the table).

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MEC-6 “DROP AND SHOOT” APPARATUS Equipment: Drop and shoot apparatus w/ two steel balls Two-way clamp, rod and base Comments: Place the two balls on the opposite ends of the apparatus and make sure the balls are level with the floor. When the spring mechanism is released, one ball will drop and the other ball will shoot to the side. They should strike the floor at the same time (as verified by the sounds of the balls hitting the floor).

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MEC-7 PROJECTILE MOTION (sometimes called monkey shoot apparatus) Equipment: Projectile motion apparatus (w/yellow plastic ball) Long metal tube and three-footed floor stand (large type) Solenoid, long brown cable and two-way clamp 10 volt Power Supply Metal can (target) and cardboard box (place under solenoid to catch target) C-clamp (to hold down the apparatus) Comments: Use the long brown cable to connect the control box (green jacks) to the solenoid (which holds the target can). Connect the red and black jacks of the control box to the red and black jacks (not ground) of the power supply – and set the output voltage of the power supply to max 10 volts (with the current knob set to max cw). The light on the support bar should be lit. It is critical that the light and photo-detector unit be adjusted such that the can will stay attached to the solenoid when the control box is set to the reset position (and also that the support bar be located as close to the end of the “firing tube” of the projectile apparatus). Place the projectile motion apparatus about 12-16 feet from the mounted target (metal can) and check that the launching tube and the target are approximately horizontal (level with the floor). Aim the launching tube by sighting down the inside of it and making sure the middle of the mounted target is visible in the cross hairs. Set the control box switch to RESET. Put the yellow plastic ball inside of the tube. Use the plunger to push the ball into the second “click” position (listen for 2 clicks). Set the control box switch to FIRE. Pull (straight) up on the string on projectile apparatus to fire the ball at the target. (Do not allow the tube to move while doing this) [NOTE - Photo below not to scale]

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MEC-8 LOOP-THE-LOOP REVISITED What speed must a ball have at the bottom of a circular loop to just make it around the loop without falling off? If the ball is to just reach the top of the ramp and not fall off, its speed must be such that the only force keeping it in a circular path is gravity. This should happen when v2 =gR. The next question is at what height (H) on the longer v-track of the loop-the-loop should the ball be released so that the ball will have enough speed to be able to complete the loop without falling off? The equation below shows that the mass of the ball cancels out and the height is related to the Radius (R) of the loop minus the radius of the ball. This is true but the interesting aspect is that the height is also dependent on the roughness or smoothness of the ball. (Does the ball slide or roll down the incline?) Two balls are provided (one smooth and rough) to show this premise. The balls have a diameter of 3.7 cm. Marks on the loop-the-loop are provided to help in locating where to release the balls. [paper pending] [Equipment: Loop the loop apparatus 2 balls- one smooth, one rough

RH

gRmRmgmvRmgmgH

25

)(212

212 2

=

+=+=

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MEC-9 SWINGING BOWLING BALL Equipment: Bowling ball with rope attached 2 long rectangular (8ft) rods, 2 table clamps, 2 two-way clamps and a long cross member steel rod Comments: The ball is mounted on a frame work (like a pendulum) above the lecture table. Pull the ball towards you until it almost touches your nose or chin. Release the ball and watch how close it returns to your nose or chin. Do not push the ball. Hold your head perfectly still. Make sure the ball does not hit anything on top of the lecture table. The ball should be about 6 inches above the table when mounted on the frame.

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MEC-10 WHIRLING BEAKER OF WATER Equipment: Plastic beaker with string attached Comments: Pour water into the beaker and swing the beaker in a vertical circle.

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MEC-11 WHIRLING CLOTHES HANGER AND COIN Equipment: Metal clothes hanger Comments: A metal clothes hanger is supplied. Take a coin (one of your) and place it on the end of the hanger. This is the end that loops over the rack bar in the closet. The hanger is bent to a modified v-shape. It may take some practice to balance the coin on the end. Spin the hanger such that the coin does not fall off (careful-do not spin the hanger in a loop towards the students). [With permission, this digital photo is courtesy of North Carolina State University – Physics.]

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MEC-12 ELASTIC AND INELASTIC COLLISIONS ON A LINEAR TRACK Equipment: Pasco linear track 2 Pasco carts (w/ springs on one side and velcro on the other) 1 black metal block (about the same mass as the cart) Comments: Make sure the track is level. May be used to show elastic and inelastic collisions.

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MEC-13 NEWTON’S COLLISION BALLS Equipment: Collision ball apparatus Comments: Apparatus has 6 balls of equal mass on strings. May be used to show conservation of momentum.

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MEC-14 CENTER OF GRAVITY WITH CHALKBOARDS Equipment: Black chalkboards (assortment) Long rod and base with a two-way clamp String and plumb bob Mounting rod (to hold boards and plumb bob) Stick of chalk and eraser Comments: Hang one of the boards on the mounting rod and place the string of the plumb bob on the mounting rod. Draw a chalk line next to the string of the plump bob. Rehang the board on another hole and draw another chalk line. Where the chalk lines intersect, the center of gravity may be found.

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MEC-15 CENTER OF GRAVITY WITH A BELT Equipment: Center of gravity device Your belt Comments: Place your belt on the groove of the center of gravity device. Illustrate the center of gravity of this system.

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MEC-16 MOMENT OF INERTIA OF A DISC AND RING Equipment: Wood board (1ft x 3ft) Spacers (2 wood blocks) Solid wood disc Thin metal ring Comments: Incline the wood board using the spacers. Place the disc and ring side by side and release at the same time. Note - The disk and ring have the same mass and the same radii. The ring (which has the greater moment of inertia) rolls more slowly than the disc. DO NOT ALLOW THE DISC OR RING TO FALL ON THE FLOOR.

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MEC-17 CONSERVATION OF ANGULAR MOMENTUM Equipment: Bike wheel with rope attached Rotating platform and attached chair 2Kg masses (2) Comments: Sit on the rotating platform while holding the spinning bike wheel in a vertical position and then turn the axle horizontally. Does this cause one to rotate on the platform? Sit on the platform and hold one of the 2Kg masses in each hand, with the arms extended from the sides. Have someone cause the person on the platform to rotate. Have the person on the platform bring in his arms to his side. Vertical precession may also be shown (by holding on to the rope that is connected to the spinning bike wheel). This should be done only while off the platform.

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MEC-18 SPOOL AND STRING DEMONSTRATION

If the string attached to the spool is pulled in the direction of the arrow, which way will the spool move (rotate) for each of the cases below? 1) Roll counter-clockwise to the left 2) Roll clockwise to the right 3) Not rotate but gets dragged on the table (in direction of arrow) [Equipment: Large spool with a string attached] A B C

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MEC-19 GYROSCOPE Equipment: Large Pasco gyroscope Slotted mass (100g) 2 strings with loops Comments: Spin the gyroscope rings with the strings provided. Attach the slotted mass to end of the gyro to show precession.

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MEC-20 FREE FALLING HINGED BOARD Equipment: Hinged board apparatus Steel ball Wood rod Comments: Position the wood rod to hold up the hinged board. Place the steel ball at the end of this board. Quickly pull out the wood rod and show how the ball will land in the cup.

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MEC-21 SIMPLE HARMONIC MOTION Equipment: Projection light source Long rod and base with motor attached Two balls attached to apparatus (one on a spring and one on the end of the motor shaft) Comments: Arrange the apparatus and the light source to project an image of the two balls on a wall. Turn on the motor and start the ball on the spring moving such that the two balls are in phase with each other.

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MEC-22 EVACUATED CAN Equipment: Vacuum pump Metal can Comments: Connect the metal can to the vacuum pump and turn on the pump. Atmospheric pressure will cause the can to be crushed.

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MEC-23 CARTESIAN DIVER Equipment: Cartesian diver in plastic bottle Comments: Squeeze the sides of the plastic bottle and watch the diver go up or down.

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MEC-24 GEYSER Equipment: Bunsen burner and flint lighter Ring stand and gauze Safety glasses Beaker with about 4 inches of colored water Gas source (on lecture table) or provide a propane tank Flask with about 50mL of water, stopper and glass tube Comments: Be sure to wear safety glasses during this experiment. Place the flask (which has a small amount of water in it) on the ring stand over the bunsen burner and heat the flask until the water boils. Pick up the flask by the insulated neck and turn it over. Put the glass tube (of the flask) into the beaker containing the water. A geyser of water will occur in the heated flask.

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MEC-25 PASCAL’S VASES Equipment: Pascal’s apparatus Extra vases Comments: BE SURE TO UNSCREW THE GLASS VASES BY THE METAL BASES (to prevent breaking of the glass). The pointer on the apparatus will be used to show that when the different vases are attached to the apparatus and the water level is raised to the pointer mark, the meter will indicate the same pressure for all vases (regardless of the shape of the vases). Before changing the vases, be sure to lower the plastic water container such that the water drains into it. [With permission, this digital photo is courtesy of North Carolina State University – Physics].

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MEC-26 ARCHIMEDES’ PRINCIPLE Equipment: 20N spring scale, short rod and two-way clamp Long rod and base Metal can with string attached Cylindrical metal block Large plastic beaker (with overflow pipe) Plastic beaker (to catch overflow water) Small plastic beaker (to help refill large beaker) Comments: First show that the metal block has the same volume as the hollow metal can by inserting the block into the can. Next, note the reading of the spring scale when the metal can and the block are hanging from it. Fill the large beaker with water up to the overflow stem. Lower the block into the beaker of water and allow the water to overflow into the plastic beaker (be sure the block is completely submerged). Now note the reading of the spring scale. Take the water that has overflowed into the beaker and pour it into the metal can (which is mounted above the block) and again note the spring scale reading.

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MEC-27 CONSTANT LEVEL TUBES Equipment: Constant level tubes with colored water Comments: The level of the water in the tubes is the same regardless of the shape of the tubes.

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MEC-28 BERNOULLI’S PRINCIPLE with a leaf blower Equipment: Leaf Blower Assortment of balls Comments: A large leaf blower is provided with an assortment of balls. One may rotate the blower at angle and show that the balls will still hover over the end of the blower.