PIRA |
Physics Lecture Demonstration MECHANICS (1J) - Statistics of Rigid Bodies |
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PIRA |
Physics Lecture Demonstration MECHANICS (1J) - Statistics of Rigid Bodies |
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1J - Statistics of Rigid Bodies
10. Finding Center of Gravity |
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| DCS # | Demonstration | Abstract/Description |
| 1J10.09 | center of gravity | Many examples of simple center of mass demonstrations. |
| 1J10.10 | map of state | Suspend a map of the state from holes drilled at large cities to find the "center of the state". |
| 1J10.10 | map of state | Sandwich of a map of the state between two plexiglass sheets and suspend from holes drilled at large cities to find the "center of the state". |
| 1J10.10 | map of Minnesota | A plexiglass map of the state is suspended from several points. |
| 1J10.11 | find the center of gravity | Use a chalk line on the plumb bob and snap it to make a quick vertical line. |
| 1J10.12 | hanging shapes | Use the plumb bob method to find the center of gravity of various geometric shapes. |
| 1J10.12 | hanging board | Suspend an irregular board from several points and use a plumb bob to find the center of gravity. |
| 1J10.12 | irregular object center of mass | Suspend an irregular object from several points and find the center of mass with a plumb bob. |
| 1J10.15 | hanging potato | Hang a potato from several positions and stick a pin in at the bottom in each case. All pins point to the center of gravity. |
| 1J10.20 | meter stick on fingers | Slide your fingers together under a meter stick and they meet at the center of gravity. Add a baseball hat to one end and repeat. |
| 1J10.20 | friction and pressure | Slide your fingers under the meter stick to find the center of mass. |
| 1J10.20 | meter stick on fingers | Slide your fingers under a meter stick to find the center of mass. |
| 1J10.25 | center of gravity of a broom | Bring your fingers together under a broom the find the center of gravity. |
| 1J10.25 | center of gravity of a broom | Find the center of gravity of a broom, hang a kg mass somewhere on the broom, find the new center of gravity, calculate the weight of the broom by equating torques. |
| 1J10.26 | balance beam and bat | |
| 1J10.30 | meter stick on fingers | |
| 1J10.30 | loaded beam - moving scales | Slide the scales together under a loaded beam noting the scale readings of the moving and stationary scales. |
| 1J10.30 | loaded beam - moving scales | Instead of moving the masses on the beam, move the scales under the beam. Same as bringing your fingers together under the meter stick. |
| 1J10.41 | your center of gravity | Two methods for measuring the center of gravity of a person are shown. |
| DCS # | Demonstration | Abstract/Description |
| 1J11.10 | leaning tower of Pisa | Add a top to a slanted cylinder and it falls down. Also hang a plumb bob from the center of mass in each case. |
| 1J11.10 | leaning tower of Pisa | A model of the tower constructed in sections. Adding the top will cause it to tip over. |
| 1J11.10 | leaning tower of Pisa | Add on to the leaning tower and it falls down. |
| 1J11.10 | leaning tower of Pisa | The leaning tower of Pisa. |
| 1J11.11 | falling cylinders | A tube, weighted at the bottom, falls when a cap is added. An upright cylinder, containing two balls, falls when a weighted cap is removed. |
| 1J11.11 | toppling cylinders | The standard leaning tower and an upright cylinder that topples when the cap is removed. It has two balls in the tube. |
| 1J11.12 | irregular object center of mass | |
| 1J11.15 | tipping block on incline | Raise an incline plane until a block tips over. |
| 1J11.15 | tipping block on incline | A very clever modification of the leaning tower of Pisa demonstration. |
| 1J11.15 | tipping block on incline | A block is placed on an incline and the incline is raised until the block tips. |
| 1J11.20 | leaning tower of Lire | Stack blocks stairstep fashion until the top block sticks out beyond any part of the bottom block. |
| 1J11.20 | leaning tower of Lire | Use 6"x6"x2' wood blocks and have a student sit under the stack as it is built. |
| 1J11.20 | leaning tower of lire | A note discussing the derivation of the harmonic series describing the leaning tower of Lire. |
| 1J11.20 | leaning tower of Lire | Use the center of mass of a composite object to support a block beyond the edge of the lecture bench. This article emphasizes a lab approach. Ref. AJP 23,240 (1955). |
| 1J11.20 | leaning tower of Lire | Stack blocks until the top block sticks out beyond any part of the bottom block. |
| 1J11.21 | cantilevered books | The number of books necessary to overhang 2,3,4, etc lengths. |
| 1J11.30 | instability in flotation | A device to raise the center of mass in a boat until the boat flips. Diagram. |
| 1J11.40 | people tasks, etc. | Pictures of three center of mass objects and several person based center of mass tasks e.g., stand on your toes facing the wall, etc. |
| 1J11.40 | male & female center of gravity | Stand with right shoulder and foot against the wall and raise your left foot. Stand with your heels against the floor and try to touch your toes. |
| 1J11.50 | double cone | As a double cone moves up an set of inclined rails, its center of gravity lowers. |
| 1J11.50 | rolling uphill | A simple version of a ball rolling up a "v". |
| 1J11.50 | double cone | A double cone rolls up an inclined "v" track. |
| 1J11.50 | double cone | Double cone and rails. |
| 1J11.50 | double cone | A double cone rolls up an inclined "v" track. |
| 1J11.50 | double cone on incline | The double cone appears to roll uphill. |
| DCS # | Demonstration | Abstract/Description |
| 1J20.10 | bowling ball stability | A bowling ball is placed in, on, and along side a large plexiglass hemisphere. |
| 1J20.11 | balance the cone | A cone can show stable, unstable, and neutral equilibrium; a sphere shows only neutral equilibrium. |
| 1J20.11 | balance the cone | A large cone shows stable, unstable, and neutral equilibrium. |
| 1J20.11 | stability | Balance a cone, show a block is stable and a sphere is neutral. |
| 1J20.12 | wood block stability | A block and support have marks that show whether the center of gravity has moved up or down when the block is displaced. |
| 1J20.15 | block on the cylinder | A rectangular block of wood is placed on a cylinder first with the width less than the radius (stable) and then with the width greater (unstable). |
| 1J20.15 | block on the cylinder | An "elementary" discussion of the oscillatory properties of the block on the cylinder. |
| 1J20.15 | block on the cylinder | A thin block on a cylinder is stable, a thick one is not. |
| 1J20.16 | catenary surface | A large block is always in stable equilibrium anywhere along this catenary surface. |
| 1J20.17 | block on curved surfaces | A block is placed on a catenary surface, a circle, and a parabola. |
| 1J20.20 | fork, spoon, and match | Place a spoon and match in the tines of a fork and balance the assembly on the edge of a glass. |
| 1J20.20 | fork, spoon, and match | Picture of the fork, spoon, and match balanced on the edge of a glass. |
| 1J20.20 | fork, spoon, and match | Stick two forks and a match together and balance on a glass while pouring out the water. |
| 1J20.20 | fork, spoon, and match | Two forks and a match can be balanced on the edge of a glass while the water is poured out. |
| 1J20.25 | nine nails on one | A technique to balance ten landscape spikes on the head of a single upright spike. |
| 1J20.30 | sky hook | A complete solution to the hanging belt problem. |
| 1J20.30 | hanging belt | Shows a "belt hook" for the hanging belt. |
| 1J20.32 | spoon on nose | Hang a spoon on your nose. Most effective with giant food service spoons. |
| 1J20.35 | horse and rider | A horse has an attached weight to lower the center of mass. |
| 1J20.35 | horse and rider | Stable equilibrium of a center of gravity object. |
| 1J20.35 | horse and rider | A horse has a weight attached to lower the center of mass. |
| 1J20.40 | balancing man | Stable equilibrium of a center of gravity object. |
| 1J20.40 | balancing man | Stable equilibrium of a center of gravity object. |
| 1J20.45 | tightrope walking | Design of a 10' long "low wire" and description of the physical feats possible. |
| 1J20.45 | tightrope walking | A toy unicycle rider carrying a balancing pole travels along a string. |
| 1J20.45 | clown on rope | A toy clown rides a unicycle on a wire. |
| 1J20.46 | tightrope walking model | A model of a tightrope walker shows the center of mass moves up with tipping. |
| 1J20.50 | balancing a stool | Wires form a support at the center of gravity of a lab stool. |
| 1J20.50 | balancing a stool | Construct a stool so that wires crossed diagonally will intersect at the center of gravity. The stool can be oriented in any direction. |
| 1J20.51 | chair on pedestal | Hide heavy weights in the ends of a chair's legs so it will balance on a vertical rod placed under the seat. |
| 1J20.55 | broom stand | Spread the bristles and a straw broom will stand upright. |
| 1J20.60 | wine buttler | Stick the neck of a wine bottle through a hole in a slanted board and the whole thing stand up. |
| 1J20.65 | glass on coin, etc | Pictures show the hanging belt, pin on the point of a needle, and a jar balanced on its edge. |
| DCS # | Demonstration | Abstract/Description |
| 1J30.10 | suspended block | Forces parallel and perpendicular to the plane will support the car midair when the plane is removed. |
| 1J30.10 | suspended block | A 3-4-5 triangle holding a block. Add counterweights and remove the incline. |
| 1J30.10 | suspended block | The components of force of a block on an inclined plane are countered by weights. The plane is then removed. |
| 1J30.10 | suspended block | A 5-6-7 suspended block system is used to show the pulleys can be moved as long as the angle remains constant. |
| 1J30.10 | suspended block | Forces parallel and perpendicular to the plane will support the car when the plane is removed. |
| 1J30.10 | load on removable incline | Place a cart on a removable 30 degree incline. |
| 1J30.15 | normal force | A block on an incline has an arrow mounted from the center of mass perpendicular to the surface with "N" on the arrowhead and another arrow hanging from the center of mass with a "g" on the arrowhead. |
| 1J30.18 | hanging the plank | A heavy plank is suspended from three spring scales in several configurations: series, parallel, and a combination. |
| 1J30.20 | tension in a string | The weight of a mass hung from a single spring scale is compared to the weight shown on a spring scale between two masses over pulleys. |
| 1J30.20 | tension in a string | A spring scale is suspended between strings running over pulleys to equal weights. |
| 1J30.21 | tension in a string | A clever story. |
| 1J30.22 | tension in a spring | Two students pull against each other through one and then two spring scales. |
| 1J30.23 | tension in springs | Masses are hung at the ends of a series of spring scales. |
| 1J30.25 | rope and three students | Two large strong students pull on the ends of a rope and a small student pushes down in the middle. |
| 1J30.25 | rope and three students | Two large strong students pull on the ends of a rope and a small student pushes down in the middle of the rope. |
| 1J30.25 | rope and three students | Two football players stretch a 10 m rope while a small person pushes the middle to the floor. |
| 1J30.25 | clothesline | Hang a 5 newton weight from a line and pull on one end of the line with a spring scale. |
| 1J30.26 | rope and three weights | Suspend a rope over two pulleys with masses on the ends and hang another mass from the center. Measure the deflection. |
| 1J30.27 | deflect a rope | Stretch a rope in a frame with a 100 newton scale measuring the tension. Pull down with a 20 newton scale. |
| 1J30.30 | break wire with hinge | Suspend a 5 kg mass from a length of wire. Break a length of similar wire by placing the same mass on the back of a large hinge. |
| 1J30.30 | breaking wire hinge | Pushing down on a slightly bent hinge will break the wire fastened to the ends. |
| 1J30.30 | breaking wire hinge | Press down on a hinge to break a rope. |
| 1J30.35 | pull the pendulum | A long heavy pendulum is displaced with a spring scale. |
| 1J30.40 | booms | A sprig scale measures the tension in the supporting rope at various loads and boom angles. |
| 1J30.40 | horizontal boom | The tension in the wire is measured with a spring scale for two different boom structures. |
| 1J30.50 | blackboard force table | Scales and masses are hung in front of a large movable whiteboard. |
| 1J30.50 | blackboard force table | A weight is hung on a string suspended between two spring scales. |
| 1J30.50 | blackboard force table | The standard blackboard force table. |
| 1J30.50 | blackboard force table | A mass is hung from the center of a cord attached to two spring scales. Start with the strings vertical, increase the angle. |
| 1J30.50 | blackboard force table | A force table in the vertical plane |
| 1J30.50 | force board | This looks like a magnetic vertical force board. A circle is marked with angles every 10 degrees. |
| 1J30.51 | vertical force table | A vertical force table that permits a continuous range of angles. |
| 1J30.51 | blackboard force table | A removable frame that sets on the chalk tray. |
| 1J30.51 | blackboard force table | A framework for doing the force table in the vertical plane. |
| 1J30.52 | force table on overhead | A plexiglass force table for the overhead projector. |
| 1J30.52 | force table on OH proj | Make a large sketch of the angles using the OH projector. |
| 1J30.53 | standard force table, etc. | The standard force table, three dimensional force table, and torque apparatus. |
| 1J30.54 | force table | Three scales and a ring to show forces add by parallel construction. Not the usual. |
| 1J30.55 | human force table | Sit on a chair that hangs from a chain attached to load cells on each end. |
| 1J30.55 | human force table | Hang from a large gallows frame on ropes attached to load cells. |
| 1J30.55 | bosun chair force table | Sit on a chair suspended from two supports equipped with protractors and commercial load cells. |
| 1J30.57 | blackboard force table - rubber band | Calibrate rubber bands for force vs. length, predict the mass of an object hung in a noncolinear configuration. |
| 1J30.57 | blackboard force table - rubber band | A simple substitute for scales is a calibrated set of rubber bands. |
| 1J30.57 | blackboard force table - springs | Use screen door springs in place of spring balances. |
| 1J30.60 | sail against the wind | Set a mainsail on a cart so it moves toward and away from a fan. |
| 1J30.60 | sail against the wind | Use a large fan to blow at an air track glide with a sail. |
| 1J30.60 | sail against the wind | A sail is mounted on an air track cart. A table fan supplies the wind. |
| 1J30.60 | sail and the wind | Apparatus Drawings Project No.4: A sailboat rides in an air trough which serves as a keel. Set the angle of the sail with respect to the wind. |
| 1J30.60 | sailing upwind (airtrack) | Use a skateboard cart with a foam core sail. |
| 1J30.61 | sail a trike against the wind | A wind driven tricycle moves against the wind. |
| 1J30.64 | sail against the wind | A wind driven boat accelerates against the wind. Description and Analysis. |
| 1J30.64 | sailboat and wind | A cork stopper boat with a keel and removable sail. |
| 1J30.65 | floating cork | A stick is hung by a thread at one end with the other attached to a cork floating on water. |
| 1J30.65 | floating cork | A stick is hung by a thread at one end with the other attached to a cork floating on water. |
| 1J30.70 | sand in a tube | Place a tissue on the bottom of an open glass tube, fill with a few inches of sand, and push down on the top of the sand with a rod. |
| 1J30.70 | sand in a tube | A couple of inches of sand held in a tube by tissue paper will support about 50 lbs. |
| 1J30.75 | stand on an egg | Three eggs in a triangle pattern in foam depressions between two plates will support a person. |
| 1J30.75 | egg crusher | A raw egg can be squeezed between two hard foam rubber pads with a force of over 150 lbs. |
| 1J30.80 | rolling wedge | A light roller lifts a heavy weight as it rolls inside an inclined hinge. |
| 1J30.90 | inverse catenary | A string of helium balloons tied at each end forms an inverse catenary. |
| 1J30.91 | catenary analog computer | Model the catenary on a simple analog computer. |
| DCS # | Demonstration | Abstract/Description |
| 1J40.10 | grip bar | A thin rod mounted perpendicular to a broom handle holds a 1 Kg mass on a sliding collar. |
| 1J40.10 | grip bar | Use wrist strength to lift a 1 kg mass at the end of a rod attached to a broom handle. |
| 1J40.10 | grip bar | Use wrist strength to try to lift 1 kg at the end of a rod attached perpendicularly to a handle. |
| 1J40.10 | grip bar | A thin rod mounted perpendicular to a broom handle holds a 1 Kg mass on a sliding collar. |
| 1J40.10 | torque bar | Use wrist strength to lift a weight suspended at various distances from the handle. |
| 1J40.15 | torque wrench | Modify a Sears torque wrench so weights can be hung at different distances. |
| 1J40.15 | torque wrench | A torque wrench is used to break aluminum and steel bolts. |
| 1J40.16 | different length wrenches | |
| 1J40.20 | meter stick balance | Hang weights from a beam that pivots in the center on a knife edge. |
| 1J40.20 | torque beam | Hang weights from a beam that pivots in the center on a knife edge. |
| 1J40.20 | torque beam | Weights are hung from a horizontal bar pivoted on a knife edge. |
| 1J40.20 | torque beam | Weights are hung from a meter stick suspended on a knife edge. |
| 1J40.20 | torque beam | Weights on a meter stick supported at the center. |
| 1J40.20 | balancing meter stick | Use a meter stick, suspended at the center, as a torque balance. |
| 1J40.21 | hinge board | Use a spring scale to lift a hinged board from various points along the board. |
| 1J40.23 | torque beam | Put a quarter (5 g) on the end of a meter stick and extend it over the edge of the lecture bench until it is just about to tip over. |
| 1J40.24 | walking the plank | Place a 50 lb block on one end of a long 2x6 and hang the other end off the lecture bench. Walk out as far as you can. |
| 1J40.25 | torque disc | Weights can be hung from many points on a vertical disc pivoted at the center. |
| 1J40.25 | torque disc | Various weights are hung from a board that can rotate freely in the vertical plane. |
| 1J40.25 | torque wheel | Use a wheel with coaxial pulleys of 5, 10, 15, and 20 cm to show static equilibrium of combinations of weights at various radii. |
| 1J40.26 | torque disc | An apparatus to show the proportionality between torsional deflection and applied torque. |
| 1J40.26 | torque disc | Twist a shaft by applying coplanar forces to a disc. |
| 1J40.27 | torque double wheel | |
| 1J40.30 | opening a door | |
| 1J40.30 | opening door | |
| 1J40.32 | opening a trapdoor | |
| 1J40.32 | opening trapdoor | |
| 1J40.40 | loaded beam | Move a weight along a 2X4 on two platform scales. |
| 1J40.40 | loaded beam | Large masses can be placed on a board resting on two platform balances. |
| 1J40.40 | loaded beam | A model bridge is placed on two platform scales and a loaded toy truck driven across. |
| 1J40.40 | loaded beam | A heavy truck is moved across a board supported on two platform scales. |
| 1J40.40 | bridge and truck | A plank rests on two spring scales forming a bridge. Move a toy truck across. |
| 1J40.41 | loaded beam | Support the loaded beam with spring scales instead of platform balances. |
| 1J40.45 | Galileo lever | Same as Sutton device. |
| 1J40.45 | Galileo lever | A simple device to demonstrate the law of moments. |
| 1J40.45 | Galileo lever | A simple device to show the law of moments. |
| 1J40.50 | Roberval balance | Large Roberval balance. |
| 1J40.50 | Roberval balance | A reminder and picture of the Roberval balance. Reaction to TPT 21, 494 (1983). |
| 1J40.50 | Roberval balance | A large model of the Roberval or platform balance. |
| 1J40.50 | Roberval balance | Neutral equilibrium is maintained at any position on the platform. |
| 1J40.51 | Roberval balance | A version of the Roberval balance where a rigid assembly has upper and lower arms on one side. |
| 1J40.55 | balances | The equal-arm analytical balance and weigh bridge. |
| 1J40.56 | balances | The steelyard. |
| 1J40.60 | suspended ladder | Model of a ladder suspended from two pairs of cords inside an aluminum frame. |
| 1J40.65 | hanging gate | A gate initially hangs on hinges, then add cords and remove the hinges leaving the gate suspended in mid air. |
| 1J40.65 | hanging gate | Construction and use of a model of the swinging gate. |
| 1J40.70 | crane boom | |
| 1J40.75 | arm model | Place a spring scale on a skeleton in the place of the biceps muscle and hang a weight from the hand. |
| 1J40.75 | arm model | Use an arm model simulating both biceps and triceps muscles to throw a ball. |