Apparent Weightlessness Flashcards
A stone of weight 3.0 N is fixed, using glue, to one end of a rigid rod.
The other end of the rod is fixed to a stationary point, and the rod is rotated so that the stone moves in a vertical circle of radius 85 cm.
The angular velocity of the rod and stone is gradually increased from zero until the glue snaps. This occurs when the tension in it is 18 N.
Calculate the angular velocity of the stone when the glue snaps
7.6 rad s^-1
Why do we perceive centrifugal force?
When a force pushes on you you either:
push back with an equal force, so you don’t change position (N1 law)
accelerate in the direction of the force (N2 law)
In this case, you are accelerating (situation b.), but since you don’t perceive a change in your position within the car, you assume you are pushing on the car with an equal force (situation a.) to the force that you can feel.
Explain why the water does not fall out of the bucket when it is upside down, if it is being swung in a circle at a high enough speed v.
The bucket experiences a force Fb towards the centre of the circle from the tension in the hand/handle
This force Fb provides a contact force Fw on the water accelerating the water towards the centre (acting against the linear velocity/momentum/inertia acting along the line of motion)
The water in the bucket has a weight W acting towards the ground
The water must experience a centripetal resultant force equal to mv2/r to travel in a circle
Provided that the speed v is high enough, the forces Fw and W acting together on the water only provide a resultant force equal to mv2/r
The forces acting on the water are enough to maintain circular motion, but not large enough to accelerate it out of the bucket
A bucket of water is whirled around in a vertical circle with radius 1.2 m.
What is the minimum speed that it can be whirled so the water remains in the bucket?
v = √(gravitational field strength x radius)
= √(9.81 x 1.2) = 3.4 ms-1
Name 3 situations where we feel weightless
Going over a bridge in a vehicle
The peak of a curve in a roller coaster
At the top of a swing
When we feel weightless do we have weight?
YES
When we feel weightlessness we have our usual contact forces?
NO
A roller coaster at an amusement park includes a ‘hump’ which is part of a vertical circle of radius r = 18.0m. A person in a car travelling over the hump feels momentarily weightless. Draw a free-body force diagram of the person and calculate the speed r at which the car is travelling.
13ms^-1
