Plug Uino Kit for Dynamics and the Speed of Sound

Transcription

1 Plug Uino Kit for Dynamics and the Speed of Sound Rails Ref Cart Ref Loads for Cart Ref Propulsion Unit/Impact Recorder Ref Support with Valve for balloon propulsion Ref Balloons (pack of 20) Ref Balloon pump Ref Chronotimer Ref Optical forks for Chronotimer Ref Microphones for Chronotimer Ref Sound making rods Ref Dynamometer 1 N Ref I Purpose Plug'Uino for the study of mechanics and sound is a simple solution that allows: a qualitative approach to the nature of linear movement the study of uniform, accelerated and constant linear movement the setting in motion of a cart measuring the speed of a cart a qualitative approach to the different forms of energy the study of energy transfers the study of a static equilibrium measurement of sound velocity in air and in a solid.

2 II Components and characteristics 1. The rail and its accessories Ref cm rail composed of three parts, two of which are deformable, with fastening notches every 5 cm to allow distance measurements 2 fixing rods (to be completed with boss heads and laboratory stands) 8 clips for fastening the three parts and holding the fixing rods 2. Cart Ref The cart is suitable for moving on the rail. Its wheels are guided in the 2 grooves of the rail. Its chassis is suitable for attaching various accessories (to be ordered separately): spring thruster, balloon thruster, shock recorder, load masses, dynamometers, etc. The cart is also usable on all ramps. The cart is delivered with the wheels disassembled. It is necessary to clip them on the hubs of the chassis taking care to respect the orientation, as on the photo opposite. 3. Load masses for the cart Ref Two loads each equal to the mass of the cart

3 4. Launcher / Impact detector Ref The system comes with a removable spring and a square bracket for mounting on the rail. (This support can be reused for the experiment on static equilibrium, or to constitute a point of attachment on the rail). With the spring, it can be fixed on the rail, using the square support, and serve as launcher. It is equipped with a ratchet and a trigger to store and release the spring energy in compression. Without the spring, it can be integral with the car and serve as a recorder of motion energy (or kinetic energy) by compressing proportionally under impact, by friction. The number of depressed notches allows a semi-quantitative study of the kinetic energy at the moment of the impact. Impact detector (without spring) Launcher (with spring) 5. Balloon launcher kit Ref A valve with air flow control that slips into the end of the balloon and clips into a holder. Two supports that attach to the chassis of the cart. One, which receives the valve, serves to secure the balloon to the cart and the other of square shape serves as a support for the balloon so that it does not touch the wheels of the cart. 6. Balloons (set of 20) Ref. 005,090 The balloon is used to propel the cart by ejection of air. 7. Pump for balloon Ref Pump to inflate the balloons in accordance with the rules of hygiene (photo is not contractual)

4 8. Optical forks and Interrupter Ref opto-electronic sensors (optical forks) attach to the rail and connect to the timer. They detect the passage of the cart equipped with the beam interrupter, and trigger or stop the timing. Supplied with a beam interrupter which, fixed to the cart, cuts the opto-electronic beam and triggers or stops the timing. 9. Microphones Ref microphones attach to the rail and connect to the timer. They detect the passage of sound waves and trigger or stop the timing. Fixed upright on the rail, they measure the duration of the sound propagation in the air. Fixed flat in contact with the rail, they measure the duration of sound propagation in the rail.

5 10. Chronotimer Ref The timer measures the transit time of the cart between two opto-electronic sensors (optical forks) fixed on the rail and connected to the device. The first occlusion triggers the timing and the second stops it. It is powered by a 9 to 12V AC adapter to avoid battery consumption. It can also measure the duration of the propagation of a sound wave between two microphones fixed on the rail and connected to the measuring device. (Illustration below). Chronotimer with connectors for forks or microphones Chronotimer trigger and stop connections Chronotimer ready to measure Chronotimer measuring

6 11. Sounding rods Ref Two metal rods 6 mm diameter x 250 mm for making sharp, reproducible sounds. 12. Dynamometers 1 N Ref dynamometers for the study of static equilibrium of the cart (sum of two forces) III Operation Connecting the rails Tilting the rail: fastening the clips to hold the rod. Tilting the rail : fixing the rod into a bosshead End stop: the fixing clip can also be used as a stop. Loads : fitting loads into the chassis Impact detector (without spring) : fixing to the chassis Launcher : fixing of the support Launcher (with spring) : fixing to the support Launcher : pressing the trigger to release the spring. Propulsion by ejection of air : inflating the belloon Propulsion by ejection of air : Inserting the valve into the neck of the balloon Propulsion by ejection of air : Fixing the balloon to the support

7 Propulsion by ejection of air : fixing the valve support to the chassis. The balloon rests on the square support Propulsion by ejection of air : opening the valve for the ejection of air Fixing the beam interrupter to the chassis Fixing the optical ffork to the rail Microphones standing (speed of sound in air) or lying flat (speed of sound in the rail) Microphones or timing forks connect to the side of the timer. To reset, press the main buttton. For the speed of sound in air, use two rods to make a sound For the speed of sound in the rail, use one rod to strike the table close to one microphone For static equilibrium, attach the dynamomters to the hooks under the chassis IV Experiments 1. Calculating the speed of the cart

8 The image above shows how to measure the time taken by the cart to go from one optical fork to the other over a distance d. Before putting the car in motion, press the reset button on the front panel of the timer, which will then wait for the 1st inerruption. 2. Study of linear motion To study the nature of the rectilinear movements, one part of the rail is tilted, the other part remaining horizontal. The two optical forks are placed in different places. For each position of these optical forks, the transit time is read and the average speed of the cart is calculated for the distance traveled. We can deduce : On the inclined part: The average speed depends on the position of the optical forks. For the same spacing, the average speed increases when the optical forks are moved downwards. On the horizontal part: The average speed does not depend on the position of the optical forks. For the same spacing, the average speed remains constant when moving the optical forks from right to left. From these experiments, one can then define what is an accelerated rectilinear motion and a uniform rectilinear motion. One can also introduce the conditions necessary for a movement to be uniform or accelerated. 3. Balloon propulsion Using the support to avoid touching the wheels, the balloon valve can be opened to allow air to accelerate one way, while the cart accelerates in the opposite direction in the same way that a rocket is propelled.

9 4. Static Equilibrium Two 1 N dynamometers are used, one end of which is fastened to the rail by means of the square mounting bracket, which is supplied with the balloon propulsion unit and the thruster / shock recorder. It is necessary to recover the support of two sets of propulsion per balloon to carry out this experiment. The other end of the dynamometers is fixed on either side of the cart. Each dynamometer exerts a force on the cart which is in equilibrium. These two forces are colinear, of opposite senses and of equal intensity (here 0.22 N). With the aid of the finger, an action is exerted on the cart to move it away from the equilibrium position. As long as the finger is in contact with the cart, it is stationary. One of the dynamometers indicates 0.40 N (in the example above) and the other 0.04 N. One can then ask the question: what are the characteristics of the force exerted by the finger? The next question is: What will happen when you remove fingers? One then removes the finger and verifies that the prediction is proven 5. Speed of sound in air The two microphones are fixed in the "standing" position at the ends of the rail formed of 2 or 3 parts. Press the reset button of the timer then strike the 2 metal strips against each other in front of the first microphone, which triggers the timing as soon as the sound wave arrives. The 2nd microphone will stop the timing as soon as the sound arrives. Reading the propagation time of the sound wave makes it possible to calculate the speed of the sound. The microphones are very sensitive, so background noise should be avoided.

10 6 Speed of sound in the rail To measure the speed of sound in a solid the microphones are fixed lying flat against the rail. 7. Three forms of energy The impact recorder (with its spring) is fixed on the rail. The cart is released from the top of the slope, descends by accelerating, continues its movement on the horizontal part of the rail at constant speed and collides with the impact recorder which is compressed. From this experiment, it can be said that if the cart gains energy of movement (or kinetic energy) in descending, it is because it loses another form of energy due to its position of elevation. On the horizontal part, losing no more "height", it retains its energy of movement until the moment of the collision. At this point its loss of motion energy is accompanied by a compression energy gain of the spring of the impact recorder/thruster. So : In ❶the cart has energy of position (potential or gravitational energy) because it is at the top of the slope. In ❷ the cart loses energy of position (or potential energy) since it decreases and it acquires, in exchange, energy of movement (kinetic energy) that increases. In ❸ on the horizontal track the cart retains the movement energy it has acquired at the bottom of the slope and its positional energy is minimal. In ❹during the collision, the cart loses its energy of movement in favour of the spring which compresses and which thus transforms this energy into compression energy (or elastic potential energy).

11 It is possible that the cart will bounce if it does not yield all its energy of movement to the spring during the shock. Applying the cart to the shock / throttle recorder, by pressing the trigger, the spring relaxes and loses its compression energy for the benefit of the cart that moves and then transforms this energy into motion energy. You can repeat this experiment by adding loads to the cart and / or increasing the slope. 8. Crash test and kinetic energy The impact recorder without the spring is fixed to the cart. The assembly forms a deformable solid comparable to a car used in crash test tests. The notched part of the shock recorder has 8 notches. The principle of the experiment is to release the car thus equipped at the top of the slope so that it comes to strike the stop which is at the end of the horizontal part of the rail. As a result of the collision, the shock recorder is compresses by a number of notches. The aim of the experiment is to show the influence of the speed and the mass of the cart on the depression of the recorder of impact and to introduce the notion of energy of movement of the cart otherwise called kinetic energy. At constant mass, the speed is varied by increasing the slope (or decreasing it). At constant speed * (therefore constant slope and at the same point of release of the cart on the slope), we load the cart with one and then two metal loads. Measurement of the velocity acquired before the impact is made using the 2 optical forks placed on the horizontal part of the rail and the timer. * The cart / rail assembly has been designed to limit friction. However low that may be, it is not totally frictionless. In particular, the addition of loads has a small influence on friction. 9. Additional experiment: equilibrium on an incline At each end of the horizontal rail, a square support (supplied with the balloon propulsion unit and the thruster / impact recorder assembly) is attached to which a dynamometer is attached. The two dynamometers are then connected to the front and rear of the cart placed on the rail. Due to unavoidable friction, one taps on the rail, to allow the cart to find its position of balance. The common value indicated by each dynamometer (here 0.85 N) is noted.

12 The rail is tilted, and after tapping on the rail (always to overcome friction), the value of each dynamometer (here 0.72 N and 0.98 N respectively) is noted. From the two experiments carried out on the horizontal and then inclined rail, a few questions arise: 1. It is observed that in each experiment the sum of the two values read on the dynamometers remains constant (here: = ). Why is this the case? 2. What is the difference between the two values read on each dynamometer? 3. Is it important to know which dynamometer indicates the greatest value? If so, what can we deduce from it? 4. If a 3rd force appears when the rail is tilted what is the cause? 5....

13 V Contact us This material is guaranteed for 2 years For all enquiries please contact: Sciencéthic 32, route de Rouen CS NORMANVILLE, FRANCE Tel.: / Fax: jecontacte@sciencethic.com / Or in the UK Science Ethic Ltd PO Box 199 Huddersfield HD8 1EL Tel / Fax sales@science-ethic,co.uk