SPEED-MANIA or how we measure the velocity in secondary-school - - PowerPoint PPT Presentation

SPEED-MANIA

• r how we measure the velocity in

secondary-school physics nowadays? István Szittyai Szeged-Hódmezővásárhely László Németh School TPI-2015, Budapest

Digital measurements

 Grammar and High School „Németh László”,

Hódmezővásárhely

 ELTE Physics Education Program (2013- )  Supervisor: prof. István Groma  Support: Noise Group (Univ. Of Szeged)  Research topic: Digital measurements in the physics

education

 Systematically look for „Where? What? How?” can we

use

 Favorite: the measurements, that is (nearly) impossible

with traditional (classical?) methods

Romania Serbia Croatia

Digital measurements

 Observation: this have additonal motivation for students!  Main difficulty: usually quite expensive …  These devices, instruments and methods are still

spreading:

 Öveges-program (renewal of the science education)  Geomatech-project (GeoGebra + some new methods)  Some other projects and funds  There are some cheap solutions, for example EDAQ 530

 Developed by „Noise Group”, University of Szeged  low-cost, compact and easy-to-use digital measurement

solution for schools

EDAQ 530 – Noise Group SZTE

• Developed in 2009-2010
• A/D converter, 12-bit, with 3 channels
• Sensors, as you want
• IR-photo-gate, pressure,

acceleration, Hall-sensor, termistors, …

• The software is free
• The hardware documentation is also

free

• Education development projects

Velocity and speed

 The concept of velocity is not an easy notion in

secondary school

 One of the first notions of physics at the age 12-13:

speed=distance/time, 𝑤 = 𝑡 𝑢

 Distance, position, displacement …  Instantaneous velocity: 𝑤 =

∆𝑦 ∆𝑢, if ∆𝑢 is „very small”

 (Velocity is a vector … now irrelevant)

Measuring velocity with IR-photogate

• Rod, straw on the moving object (thickness: 𝑒)
• Level-crossing detector „on” (in the software)
• Speed is calculated from ∆𝑢 and 𝑒
• !!! We measure the inst. velocity !!!

(if d is small enough …)

Foucault-pendulum (period,

• grav. constant, energy loss)

Group of students (age 12-13), measuring the velocity with photo-gate

Ruler with insulating tape

Measuring acceleration! (in particular: 𝑕)

Ultrasonic motion sensors

The software generate the velocity-graph from the distance-graph

Collison on the air track (2 gliders, moving in the same direction)

Motion on a slope (air track with a spring on the bottom

Measuri suring ng ref efracti active in index x - - speed eed of

• f li

light ht in in li liquids uids

WITH LASER DISTANCE MEASURE

The instrument

 Model: Toolcraft LDM 50 T  Red laser (𝜇 = 650 nm)  Range: 5 cm – 50 m  Accuracy: ±1.5 mm  Operation: time-of-flight principle

(𝑡 = 𝑑𝑢)

 20 results can be stored  Continous measurement

The method and notations

 The speed of light in air: 𝒅  The inner height of the tube: 𝒆  The height of water: h  Flight time: 𝒖 (or 𝒖/𝟑)  The value measured by the instrument:

𝒕(> 𝐞 ‼). (Clearly: 𝑡 = 𝑑𝑢)

 Refractive index of water: 𝒐  Some computation: 𝒐 =

𝒊+(𝒕−𝒆) 𝒊

 𝒕 𝒊 =

𝒅 𝒘 − 𝟐 𝒊 + 𝒆 = 𝒐 − 𝟐 𝒊 + 𝒆

𝒊 𝒆

A mérési elrendezés

Refractive index of water

s = 0,3486h + 0,5251

0.450 0.500 0.550 0.600 0.650 0.700 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 S (m) h (m)

s(h) diagram

n=1.3486

Refractive index of some

• ther liquids
• With the same method
• Vegetable oil: 𝑜 ≈ 1.47
• Glycerol: n ≈ 1.48

Measuring the speed of sound

DIRECTLY WITH SOUND INTENSITY SENSORS

Speed of sound in air

 If you have two sensors, connected to a date-logger  The distance: 𝑒  Make some sudden noise from the side  Thanks to the high sampling rate we can determine the

delay (Δ𝑢) between the signs

 And from this, calculate the speed: 𝑑 = 𝑒/Δ𝑢  Its simple, fast and accurate enough in school  In water??  In other gases?

Speed of sound in carbon-dioxid

• Inge H.A. Pettersen: Speed of Sound in Gases Using an Ultrasonic

Motion Detector, The Physics Teacher 40, 284 (2002)

• Calibration of the ultrasonic detector: 343 𝑛/𝑡 at 20℃
• The speed in 𝐷𝑃2: 268 𝑛

𝑡 (at 24℃ )

• Investigation of temperature variations in the speed

Result graph

Thank you for your attention!