Lecture Demonstrations

Martin SimonGueorgui GueorgievKrysten Cunnigham

http://www.physics.ucla.edu/demoweb/

• \demoweb\images\astronaut.mov

Is this true? I have read in books that when you get into space there is no gravity.

• Liquid Nitrogen

• melting temperature:

77K, -196C, -320 F• density 1.3g/L

Gas Atmosphere Boiling point Melt

Nitrogen 78.1% 77 K, -196 C, -320 F 63 KOxygen 20.9% 90 K, -183 C, -297 F 54 KArgon 0.9% 87 K, -186 C, -303 F 84 K

Carbon Dioxide 0.038% 195 K,-78 C, -108 F Helium 4.2 K, -269 C, -452F 0.95 K Water varies 373 K, 100 C, 212 F 273 K

Heat of Fusion (melting) Heat of VaporizationWater 335 kj/kg 2260 kj/kgNitrogen 25.5 kj/kg 201 kj/kg

DensityNitrogen 1.3 g/lOxygen 1.4 g/lCarbon Dioxide 2.0 g/lHelium 0.2 g/l

• Doppler shifts– doppler horn – ephysics\physlets\doppler_shift.htm

Ping-Pong Cannon

1 atm = 760 mmHg (Torr) = 14.7 lb/in2

1 lb = 4.448 N1 m = 39.37 inspeed of sound = 343 m/s at 200C

ping-pong ball: diameter = 1.45 in mass = 1 g = 0.001 kgtube length = 68 in

with P = 14.7 lb/in2 W = F*d = (14.7 lb/in2)(* 0.722 in2)(68 in) = 1628 lb in = 183 JW = K = ½ * m * v2 or 183 = ½ * 0.001 * v2

v = 604 m/s

• Singing Rod Standing Waves

• Driven Damped Harmonic Oscillator– Equation:

– Solution:

)cos(02

2

tFkxdt

dxb

dt

xdm

)sin()(

)( 022222

02

0

tmbm

Ftx

• Capacitor • Two Conductors (ie metal plates) separated by an

insulator (example, air) stores charge and energy

Large Capacitor 400 µF 6 kV 7200 joules

Defibrillator Capacitor 70 µF 5 kV 875 joules200 joules to the body in 2 ms = 100 kW20 amps at 5 kV for 2 ms

20 mA can cause muscle contractions70 mA across torso – heart goes into ventricular fibrillationhigher currents cause heart to stop and usually restart

Dry skin resistance 10,000—1,000,000 Ohms Wet skin 1,000 OhmsWet skin in contact with 120 V power line-- 120/1000 = 120 mA

• Tesla Picture

• ePhysics – UCLA’s online electronic physics demonstrations

• Webpage - http://ephysics.physics.ucla.edu/

– ephysics\physlets\1.1\elenses_and_mirrors.htm

• Sulfur Hexafluoride• Molecular weight 146g/mol• 5 x density of air

• Helium• Molecular weight 4g/mol • 1/7 density of air