18) Did you see the movie 2001 Space Odyssey (1968) ?
The hero can walk inside his space ship even though there is no real gravity due to a planet ?
This is possible if you create artificial gravity. If the space ship were
to rotate about an axis located in the middle of the ship, artificial acceleration would be created.
You would be walking on the wall of the ship.

If the ship has a circular motion around its axis, there is a centripetal acceleration ac:
V²/R. V is the orbital speed and R is the radius. From the point of view of the astronaut, there are 2 forces balancing each other. (inside the ship). The centrifugal force Fc (mV²/r) pulling him outward and the normal force N from the wall. You can find the right speed V and the right radius R so the acceleration ac is exactly  9.8m/s/s.
ac = V²/R = 9.8 m/s/s
If your space ship has a radius of 200m (R = 200 m),
Find the speed V = ________ m/s
(just plug the numbers in the expression of ac)
Convert into mph : V = ____________ mph
(1 mile = 1,600m and 1 hour = 3600 seconds)
What would be the period T ? (time for the ship to go one revolution? )
(use V = 2pi R / T , pug it in, plug it in !) T = ______________ s
Compare to EArth period of revolution _______________________________________


19) Actually, if the spaceship accelerated in a straight line, you won't see the difference between the EArth gravity and the artificial gravity.  You will be able to walk on the wall.
THe acceleration is no more the centripetal acceleration but,  from your point of view, you are in equilibrium between 2 forces: The normal force from the wall N and the pseudo force F = ma. (you feel this kind of force when you are in an elevator, in a car braking or in the NYC subways).
The space ship will have to accelerate, to the right, at a rate of 9.8m/s/s.
(its speed increases by 9.8m/s every second).
From this situation, the ship suddenly, accelerates downward (with the same acceleration).
After you recover from your fall, where will you be ? draw the fall and the new situations.
 Extra credits for nice and neat drawing. Comic style.

20) AS explained in class, if you work in a referential inside the object going into circle, the force pushing the object outward is called the centrigugal force. If you are in a car and make a turn you really feel this outward force. Your security belt balanced it to keep you on your seat. Physicists, sometime argue that the force is a pseudo one. It does not really exist but you really feel as you make a sharp turn ! isn't it? The frictional force on the tire prevents your car to fly off the road. If the frictional force is not large enough, off you go. (as soon as you stop turning, the centrifugal force vanishes and you fly along the tangent of the curve).

From the car referential, 2 forces act on the car. The centrifugal force Fc= mV²/R and the frictional force
fr between the tires and the road pushing inward. R is the radius of the curve. If the frictional force can't balance the centrifugal force , off go the car, along the tangent of the curve (same direction as the vector V).
A) If you double your speed V, the centrifugal force ______________________________________
(hint: use Fc = mV²/R, replace V by 2V, what will happen to Fc' ?)
B) If you double the radius of the curve (less sharp), the centrifugal force ______________________
(hint: use Fc = mV²/R, replace R by 2R, what will happen to Fc' ?)
C) conclusion: If the curve is sharp, and if you don't want to fly off, you need to ______________

D) When a pilot makes a sharp turn, he too feels this force (Fc ). The force should not exceed about 10 times his weight.
That is the acceleration should not exceed 10 times 9.8m/s/s. Otherwise, the blood pressure can't bring the blood tot he brain and he may faint. Ordinary people have a very hard time to stand more than about 8 times the gravity. Pilots must be trained to stand it.
If a pilot makes a turn with R =200m and the acceleration "he feels"is twice the acceleration due to gravity. (that is the force he feels  is twice his weight), Find the speed in km/s then in mph . V = __________km/s = __________mph
(hint use ac = V² / R with ac = 2 g , of course g = 9.8ms/s, solve for V)

21) To make an atomic bomb you need to extract Uranimu 235 from other Uranium components, more heavy.
What is the device they use to do that ? (has some connection with what we are learning ) ?

22) do that experiment in class (see picture). Try to lift a 1 kg using just a tube an a string:


FRom the point of view of the rotating mass, 2 forces act. The centrigugal force and the weight of 1 kg. IF the speed is large enough, the centrifugal force _________ and the mass can be _______

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