Unit 3 - Stability, Moments and Hydraulics Flashcards
Where would the centre of mass of an object be if it was stable?
Within the baseline. A line vertically down from the centre of mass is called the line of action of the weight. If this is within the baseline the object is stable, it won’t topple even when given a small push.
Describe the resultant moment acting on a stable object.
It is zero! The clockwise moment = the anticlockwise moment.
Why are liquids used in hydraulic systems?
They are virtually incompressible so transmit (move) pressure equally in all directions.
Give two ways of making a child’s high chair more stable.
Increase the distance between the legs to widen the baseline.Decrease the length of the legs.Fix a mass to the bottom of the chair.Last two both lower the centre of mass of the object.
A pendulum swings 5 times in 10 seconds.What is the time period?What is the frequency of the pendulum?
Time period = 2 secondsFrequency = 1/2 = 0.5 Hz
I know what moment means in the phrase ‘moment of a force’.
The turning effect.
A fisherman holds his 2m long fishing rod at one end. A fish is caught on the line and exerts a force of 20N. What is the moment of the force produced by the fish? Add the unit.
2 x 20 = 40 Nm
Describe the size of the clockwise and anticlockwise moments acting on a see saw which is balanced.
The clockwise moment = anticlockwise moment. There is no resultant moment.
Define centre of mass.
Where the mass of an object APPEARS to be concentrated.
Why does a force multiplier system like hydraulic brakes increase the force input?
The area of the slave piston is larger than the master piston. Equal pressure multiplied by larger area = a larger force.
What happens to a pendulum bob in one cycle?
It swings from one high point to another AND BACK AGAIN.
If a pendulum has a frequency of 5Hz what is happening?
It completes 5 cycles in a second.
What is the time period of a pendulum with a frequency of 0.25 Hz?
T = 1/f = 4Hz
Explain why a object is unstable and will topple.
The line of action of its weight lies beyond the baseline CAUSING a resultant moment to act on the object.
