Slides in this set
· To undo a tight wheel-nut on a bicycle you need a spanner, the
longer the spanner handle the less force you need to exert to
untighten the nut.
· The turning effect of the force is called the moment of the force, it
can be increased by:
· Increasing the size of the force
· Using a spanner with a longer handle.
· The weight is called the load and the force of the person is called
the effort. The point at which the lever turns is called the pivot.
· To work out the moment:
Moment (Nm)= force (N) x perpendicular distance from the pivot to
the line of action of the force (m)…read more
CENTRE OF MASS
· The centre of mass of an object is the point where its mass may be
thought to be concentrated.
· If you suspend an object and the release it, it will come to rest with its
centre of mass directly below the point of suspension. The object is then
in equilibrium, its weight does not exert a turning effect on the object
because of its centre of mass is directly below the point of suspension.
The centre of mass of a symmetrical object:
· If an object has more than one axis of symmetry, its centre of mass is
where the axes meet.
· To test for where the centre of mass is you:
Get a stand and hang a piece of card from the stand then hang a plumbline
(a piece of string with a small weight at the end) and from whatever point
you hung the card from draw a line in the same place the string is when its
hanging, then do this from another point and the point where the lines
bisect each other is the centre of mass of the object.…read more
MOMENTS IN BALANCE
A model seesaw:
· An clockwise moment due to W2 about the pivot = W2d2
· The anticlockwise moment due to W1 about the pivot = W1d1
· W 1d1 = W 2d2
· The principle of moments, this states that, for an object in
The sum of all the clockwise moments about any point = the
sum of all the anticlockwise moments about that point…read more
Stability and safety:
· Lots of objects are designed for stability do they don't topple over easily.
1. Tractor safety:
· A tractor on a hillside won't topple over because the line of action of its
weight acts within its wheelbase, if it's tilted more it will topple over,
when the line of action of its weight acts outside the wheelbase.
The bus test:
· A double decker bus is tested to see how much it can tilt without toppling.
These tests are important to make sure that buses are safe to travel on ,
especially when they go round bends and on hilly roads.
3. High chair:
· A high chair needs a wide base, when the child is sitting in it the centre of
mass is above the seat, if the base is too narrow the chair will topple if the
child leant sideways too much.…read more
· For an object moving in a circle at a constant speed, at any instant:
· The objects velocity is directed along a tangent to the circle.
· Its velocity changes direction as it moves round.
· The change in velocity id toward the centre of the circle.
· The object therefore accelerates continuously towards the centre of the
circle, so the force on an object acts towards the centre of the circle.
· Any object moving in a circle must be acted on by a resultant force that
acts toward the centre of the circle, we call this the centripetal force
because it always acts toward the centre of the circle.
· The centripetal force on a car going round a round about is due to friction
between tyres and the road.
· The centripetal force on an aeroplane circling round is due to the
combined effect of its weight and the lift force on it.
Centripetal force factors:
· The centripetal force needed increases if the speed
· The centripetal force needed increases if the radius
of the circle is decreased.…read more