1© manhattan press (h.k.) ltd. weightlessness artificial gravity artificial gravity 5.7...

© Manhattan Press (H.K.) Ltd. 1

• WeightlessnessWeightlessness

• • Artificial gravityArtificial gravity

5.7 Weightlessness and 5.7 Weightlessness and artificial gravityartificial gravity


Weightlessness5.7 Weightlessness and artificial gravity (SB p. 191)

Feels weightless in spaceship- moving with uniform circular motion around earth in space

centripetal force - by total weight of spaceship and astronaut


Weightlessness5.7 Weightlessness and artificial gravity (SB p. 191)

For whole system

grvrvmMmgMg

2

2

For astronaut only

0

2

RrgrmRmgrmvRmg

No reaction on astronaut

(weightless)


Artificial gravity5.7 Weightlessness and artificial gravity (SB p. 192)

Artificial gravity- help astronauts to stay long time in space

1. Wheel-like space station

2. Two rotating space capsules with central connecting axis


5.1 Angular velocity and linear velocity5.1 Angular velocity and linear velocity

5.7 Weightlessness and artificial gravity (SB p. 193)

1. For a mass moves in a circle from A to B, the radius r subtends an angle θ at the centre of the circle. The angle θ can be measured in radians or degrees. It is known as angular displacement:

where s is the length of the arc.

rs


5.1 Angular velocity and linear velocity5.1 Angular velocity and linear velocity


2. The angular velocity () of the mass is defined as the rate of change of angular displacement.

where t is the time interval. The unit of is radians per second (rad s–1) or revolutions per second (rev s–1).

3. The linear velocity of the mass is:

v = r

t


5.2 Centripetal acceleration and force5.2 Centripetal acceleration and force


4. An object in uniform circular motion experiences centripetal acceleration which is the acceleration directed towards the centre of the circle.

5. Centripetal acceleration (a) is:

rvrva

22


5.2 Centripetal acceleration and force5.2 Centripetal acceleration and force


6. Centripetal force (Fc) is:

7. For a uniform circular motion:Centripetal force is always perpendicular to the motion of the body. It does no work on the body and the kinetic energy of the body remains unchanged.

mvmrrmvF 2

2

c


5.3 Vehicles rounding bends5.3 Vehicles rounding bends


8. When a vehicle turns around a corner, the sideway friction between the tyres and the ground provides the centripetal force that enables the vehicle to follow the curved track. The maximum speed of the vehicle is independent of its mass.

9. When a vehicle turns around a banked bend of angle θ, the centripetal force is provided by the components of the normal reactions towards the centre of the curve bend.

rgv2

tan


5.4 Aircraft turning in flight5.4 Aircraft turning in flight


10. In a level flight, an aircraft experiences a lifting force (L), which is perpendicular to the surface of its wings. It balances the weight of the aircraft (mg).

11. To turn around, the aircraft must tilt an angle θ, so that the horizontal component of the lifting force provides the necessary centripetal force, and its vertical component balances the weight of the aircraft.

The tilting angle depends only on the aircraft’s speed and the radius of the turn.

rgv2

tan


5.5 Looping the loop (Motion in a vertical 5.5 Looping the loop (Motion in a vertical circle)circle)12. Consider a particle of mass m revolving at a

constant speed v in a vertical circle of radius r by means of a string. The tension at the bottom is a maximum and that at the top is a minimum.



5.6 Centrifuge5.6 Centrifuge

13. A centrifuge consists of microcentrifugal tubes which are freely hinged at a pivot and rotated at a high angular speed in a horizontal circle. It is used to separate suspension particles from the liquid or liquids of different densities.



5.7 Weightlessness and artificial gravity5.7 Weightlessness and artificial gravity

14. An astronaut feels weightless in a spaceship which is moving with uniform circular motion around the earth in space.



End

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