Using physics to make things work Flashcards
What is a moment?
A moment is the turning effect of a force.
What equation gives the size of the moment?
M = F x d
M is the moment of the force in newton-metres, Nm
F is the force in newtons, N
d is the perpendicular distance from the line of action of the force to the pivot in metres, m.
What two things can be done to increase the moment?
1) Either the force must increase.
2) Or the distance to the pivot must increase.
Why is it easier to undo a wheel-nut by pushing on the end of a long spanner than a short one?
It is easier because the long spanner increases the distance between the line of action of the force and the pivot.
Why is a lever used?
When using a lever what is the name of the force that we are trying to move?
What is the force applied to the lever called?
What does the lever do and how does this help the user?
We use a lever to make a job easier.
When using a lever the force we are trying to move is called the load and the force applied to the lever is the effort.
A lever acts a force multiplier, so the effort we apply can be much less than the load.
What is the centre of mass?
The single point where the mass of an object can be thought of as being concentrated.
What will happen to any object that is freely suspended?
What is the object in at this point?
Any object that is freely suspended will come to rest with its centre of mass directly below the point of suspension, the object is then in equilibrium.
How can the centre of mass of a thin irregular sheet of material be found? (5)
1) Suspend the thin sheet from a pin held in a clamp stand, because it is freely suspended it is able to turn.
2) When it comes to rest, hang a plumbline from the same pin.
3) Mark the position of the plumbline against the sheet.
4) Hang the sheet with the pin at another point and repeat the procedure.
5) The centre of mass is where the lines that marked the position of the plumbline cross.
On what does the centre of mass depend and where can it sometimes be?
For a symmetrical object where is the centre of mass?
What if object has more than one axis of symmetry?
The centre of mass depends on the shape of the object and can sometimes lie outside the object.
For a symmetrical object, its centre of mass is along the axis of symmetry.
If the object has more than one axis of symmetry, the centre of mass is where the axes of symmetry meet.
What can be said about an object that is in equilibrium? (3)
1) It is balanced.
2) It is not turning.
3) Total clockwise moment and total anti-clockwise moment are equal.
Give two everyday examples of the principle of moments.
1) Seesaws
2) Balance scales
Through what does the line of action of the weight of an object act?
What will happen if the line of action of the weight lies outside the base of an object?
The line of action of the weight of an object acts through its centre of mass.
If the line of action of the weight of an object lies outside the base of an object, there will be a resultant and the object will tend to topple over.
What two factors will increase the distance an object has to tilt before the line of action of the weight moves outside the base?
1) Wide base
2) Low centre of mass
By what equation is pressure given?
P = F/A
P is the pressure in pascals, Pa (or N/msquared)
F is the force in newtons, N
A is the cross-sectional area at right angles to the direction of the force in metres squared.
What can be said about liquids with regard to compressibility?
How is pressure transmitted in a liquid?
What does this mean about a force exerted at one point on a liquid and where is this made use of?
Liquids are virtually incompressible and the pressure in a liquid is transmitted in all directions.
This means that a force exerted at one point on a liquid will be transmitted to other points in the liquid. This is made use of in hydraulic pressure systems.
