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The Force What is it? Is It With Us?

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Newton’s Laws of Motion Newton’s Law of Gravity

• An object remains at constant • Gravity always exerts a force velocity unless acted on by a net • The force causes an acceleration force • An object falling in Earth’s gravity field has constant acceleration • The net force is equal to the mass • Unless air resistance is accounted for, when the times the acceleration (change in the acceleration varies velocity with time) • The weight of an object is the force of gravity on the mass • For every action, there is an equal • Weight is not the same as mass! and opposite reaction https://youtu.be/jwPc0kK9VHU

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Velocity and Acceleration Cartoon Physics

• Velocity is the speed in a • A character only falls under gravity when they given direction realize that they are about to fall. • https://www.youtube.com/watch?v=wRSHzenjiNA • Acceleration is the rate of change of velocity with time

• They are different and can even be in opposite direction!

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What Actually Happens The Movie “Speed”: Bus Jump

• Parabolic (curved trajectories) https://www.youtube.com/watch?v=dKJa-KQNjQU • Acceleration due to gravity constant • Is it good physics? • Horizontal velocity constant • What minimum launch angle is needed to get • Does not depend on the mass across a 16 metre gap at 116 km/h? • https://phet.colorado.edu/sims/html/projectile- motion/latest/projectile-motion_en.html

휃 Δ푥 = 16 푚

−1 푣푖 = 116 푘푚. ℎ (70 푚푝ℎ) Angle of 4.5o needed 9:33 AM 7 9:33 AM 8

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• Notice that the missing bridge section is horizontal, so the bus would launch horizontally

Bus has mysteriously tilted upward on launch!

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Superman Superman Flying

• Can fly • Force of gravity pulls Superman downwards • • Very strong Must be a force acting upwards to make him hover. • Must be generated by Superman • X-ray vision Anti-Gravity

Gravity

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• Suppose Superman is flying through the air • Needs a propulsive force as well as the antigravity Superman Catching Lois force • Superman catching her – deceleration causes Anti-Gravity enormous force.

Propulsion Air Resistance

Gravity

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• Newton’s Second Law restated:

퐹표푟푐푒 = 푚푎푠푠 × 푎푐푐푒푙푒푟푎푡𝑖표푛 Catching the Helicopter

• Giving us

푚푎푠푠 × 푐ℎ푎푛푔푒 𝑖푛 푣푒푙표푐𝑖푡푦 퐹표푟푐푒 = 𝑖푛푡푒푟푎푐푡𝑖표푛 푡𝑖푚푒

50 푘푔 × 20 푚/푠 퐹표푟푐푒 = = 20000 푁 0.05 푠 Superman has antigravity AND antitorque

Equivalent to having 40 times your own weight land on you! 9:33 AM 15 9:33 AM 16

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Visible Laser Beams LASER

Goldfinger – the Evil Genius • Light Amplification by Stimulated Emission of Radiation with a death ray https://www.youtube.com/wa • A photon (wave packet of light) tch?v=Mx9z99YJ_7s encounters an atom in an excited quantum state (electron in high 퐸2 energy level)

Ocean’s Twelve - the burglar alarm • If the energy of the photon matches https://youtu.be/mr834Cs9ncs the difference in energy between two levels then 퐸1 • Stimulated emission takes place 9:33 AM 17 9:33 AM 18

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LASER Helium Neon Laser

• Light Amplification by Stimulated Emission of Radiation • Uses excited Helium atoms to collide with the Neon. • The Neon does the emission

• Stimulated emission: The excited level

• 2 identical photons Red light 3푠 → 2푝

• Moving in the same direction as the original one

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• If there are particles that can scatter the photons, • The photons move in a straight line. then you can see the beam from the side • You can only see the beam, if you look directly • Dust along it (bad idea) • Aerosol droplets • Water vapour • Dry ice particles

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The Reality Exploding Cars Falling Off Cliffs

• Industrial Laser for cleaning metal

https://www.youtube.com/watch?v=Q8q3DZB_l6M

• Dr No scene • Beam visible because of rust particles being burned off the surface • https://www.youtube.com/watch?v=RO88NI16g84&feat ure=youtu.be

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• The fuel in a car is relatively safe • An explosive mix requires a mix of the vapour and Explosions air in a fairly narrow ratio • A sudden release of energy • Explosive mix 1.5 – 7 % fuel to air ratio resulting in flames (usually) and a • Sparks needed pressure wave moving outwards from the source taking fragments • with it. Realistic car falling off a cliff https://www.youtube.com/watch?v=O9197iNEGSo “Freedom” 1982 – Scott Hicks • In Movies, watch for: • https://youtu.be/xmsnSRoWdUo • People outrunning explosions • Simultaneous flash and sound • Selective directions of the pressure wave resulting from the explosion 9:33 AM 25 9:33 AM 26

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The Speed of Sound versus the • Speed of light 푐 = 300,000,000 푚푒푡푟푒푠 푝푒푟 푠푒푐표푛푑 Speed of Light • Speed of sound in air 푣 = 330 푚푒푡푟푒푠 푝푒푟 푠푒푐표푛푑 • Not what happens in explosions in movies –usally simultaneous. Light arrives • What actually happens: very quickly https://youtu.be/D9CxYQ7OHB4 The sound • See the flash first travels more • Then hear the sound slowly and arrives after the light

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Iron Man Running From Explosions

https://youtu.be/0R3N5ByTnIM?t=55 • Explosion sound and flash • No shockwave from the explosion • A rapid release of chemical • Sparking bullets (they don’t) energy into hot gases • https://youtu.be/3o2ACEr9NmQ?t=85 • Forms a pressure wave which moves rapidly • Several thousand m/s

• You can’t outrun it… Usain Bolt 100 m in 9.58 s = 10.4 m/s

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Pirate Treasure Density

• “How much stuff there is in a given volume” Moving very heavy objects • The definition of density is 푚푎푠푠 푑푒푛푠𝑖푡푦 = 푣표푙푢푚푒

Blackbeard the Pirate (1952) https://youtu.be/DwLnjw1ey7Q?t=2879 • We measure this in grams per cubic centimetre or kg per cubic metre

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• When the unit of the gram and the centimetre • Pearl density 2.6 g/cm3 were defined, the values were fixed so that the density of water would be 1 gram per cubic • Estimate the volume of centimetre the chest in the movie Material Density (grams per cc) clip

Balsa wood 0.12 3 Cork 0.25 푉표푙푢푚푒 = 60푐푚 × 40푐푚 × 40 푐푚 = 96,000 푐푚 Gasoline/petrol 0.72 Float on water Ice 0.92 Human body 0.995 푚푎푠푠 = 푑푒푛푠𝑖푡푦 × 푣표푙푢푚푒 Water (fresh) 1.0 Pearls 2.6 – 3.0 Aluminium 2.7 3 Iron 8.0 푚푎푠푠 = 2.6 × 96,000 푐푚 = 249,600 푔푟푎푚푠 Sink in water Silver 10.4 Lead 11.3 Gold 19.7 푚푎푠푠 = 250 푘푔 , 푎 푤푒𝑖푔ℎ푡 표푓 550 푝표푢푛푑푠 9:33 AM 33 9:33 AM 34

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Star Wars The Kessel Run

• Is the Force really with us? • https://www.youtube.com/watch?v=fjYuw6zWk_Y &feature=youtu.be

• Talking about a fast ship… • Mentions it can do the Kessel Run in 12 parsecs (implying fast) • Unfortunately, the parsec is a unit of distance, not time.

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• The parsec is the distance to Doing the Kessel Run a star, if the parallax angle is 1 second of arc • https://www.youtube.com/watch?v=6LBCr4tTnPo

• Equivalent to 3.26 light-years • Sound in space or • Visible laser beams • 31 × 1012푘푚 • Slow light pulses • 31,000,000,000,000 푘푚 • Banking Spacecraft

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Sound Waves What Are Those Guns Firing?

• https://youtu.be/wtoHjGWc2s8?t=96 • Lasers can’t be seen from the sides • Travel much too fast to be seen • Charged Particles? • Still travel very fast • Tracer bullets? • Energy transfer between air molecules • Can’t have sound where there are no molecules! Royal Navy training film 27624 https://www.acs.psu.edu/drussell/Demos/waves/wavemotion.html https://youtu.be/ip3-4vhVnIE?t=634

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Atoms and Molecules • A solid is lots of atoms strongly bonded together. • An atom is the basic building block of matter • A liquid is lots of molecules fairly close together, but only weakly • The atom comprises of a small bonded. They can move around, nucleus with negatively charged and the fluid can flow electrons moving around it • The nucleus has protons • A gas is a collection of atoms or (positively charged) and molecules which are very weakly bonded, usually at long neutrons (no charge) in it distances from each other, and highly mobile • Atoms may bond together to form molecules 9:33 AM 41 9:33 AM 42

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Plasma: The 4th State of Matter Spacecraft Banking Whilst Turning

• The atoms are ionized, so there is a charged • Aircraft need to do this to turn in the atmosphere “gas” • In space there is no atmosphere, so the spacecraft • https://youtu.be/EDD360PgDRg does not need to bank, just fire an engine in the • How do you keep the plasma in one place? appropriate direction • Magnetic fields: but they would interfere with nearby plasma charges! X-wing: https://youtu.be/ntG28o6DhcY

What they should do: Babylon 5 Star Fury https://youtu.be/nanfQ0mviaU

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• The lift force from the wing is partly directed to the centre of the turn Giant Creatures • This pushes the aircraft round in a circle

• Only works if there is air flowing over the • Them! wings • Giant ants (1954) • Useless in space • https://youtu.be/KPw4U_IhWV4 where there is no air • The chitin exoskeleton of an insect is not strong enough when you scale up in size

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Giant Humans Hydrostatics

• https://www.youtube.com/watch?v=h_ZDlJ61erY • Pressure increases as you go further down in a fluid • Blood Pressure in the legs • Due to the weight of the fluid above you exerting an extra • Heat Regulation pressure

푃 = 푃푠푢푟푓푎푐푒 + 휌푔푑

Density of fluid Acceleration due Depth below the surface 9:33 AM 47 9:33 AM to gravity 48 47 48

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• Apply this to the human body • Assume no fluid flow (small The Incredible Shrinking Man correction needed for flow) https://www.youtube.com/watch?v=VnDfrveCADo Measure blood pressure at the shoulder • What happens to the mass? Similar height to the heart. • Smaller atoms? • Smaller atomic bond lengths?

• Shrinking the atom would require different charges and Blood pressure at the legs masses of the protons, must be higher, since the legs neutrons and electrons are lower down

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• If the weight stays the same, it all acts on a much • Changing chemical bond smaller area – the floor would deform! lengths to shrink the molecules? 퐹표푟푐푒 푃푟푒푠푠푢푟푒 = • Again, change the mass and 퐴푟푒푎 charge of the atoms. • Has nasty problems because the shape of molecules is extremely important • DNA spiral changes If the feet are ½ in both dimensions, then the area is ¼

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Creating New Elements Periodic Table • http://www.rsc.org/periodic-table/history • What you have to do – have a nucleus with more protons in it – the number of protons determines Creating Darmstadtium the chemical element Element 110

• Looks easy in the movies:

• https://youtu.be/y0brSA1cyzw

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The Absent Minded Professor: Conservation of Energy Flubber • Energy cannot be created or destroyed. • A ball that bounces higher when dropped! • Maybe converted into different forms • https://www.youtube.com/watch?v=QrwqIEIQuoY &feature=youtu.be

• Actual bouncing ball • The Flubber would need to gain energy from • Loses height on each bounce – energy loss elsewhere – maybe remove heat from the floor • Losses to sound, ball getting warmer • Or the Flubber could cool down to compensate. But • https://www.youtube.com/watch?v=aY3TrpiUOqE then it would freeze eventually.

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Breaking Glass With Sound - • Some things oscillate with only one natural frequency Resonance • Mass on a spring • Natural Frequency of Vibration • External vibration at exactly the same frequency • Causes high amplitude vibration • Some things oscillate with a • Can break things harmonic series of frequencies • Waves on a string

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• A wineglass has a set of natural frequencies, when the glass Limitless Image Enhancement vibrates • Check this by tapping the glass • Blade Runner (1979) • Now use a sound wave of exactly • that frequency to make the https://www.youtube.com/watch?v=hHwjceFcF2Q oscillation very big. • An example of quantization – the picture consists of https://youtu.be/JiM6AtNLXX4 many discrete elements.

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3892 by 3265 pixels 14 by 9 pixels

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And Finally: Spiderman

• https://youtu.be/nGAyUqgtUas

• Bad Physics: Spiderman must fall at the same rate as Mary-Jane unless he is in powered flight • Good Physics: Spiderman catches up to Mary Jane so the impact is minimized • Good Physics: Conservation of energy with the elastic spider web to slow them down Enjoy the Movies: even if the physics is not so good

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