FM1 - Turning forces, centre of gravity and moments Flashcards
What is a moment?
The turning effect of a force
What is the equation linking moment, force and distance?
Moment(Nm) = Force(N) x perpendicular distance (m) (between line of action and pivot)
Explain what happens with a spanner and a nut (force? moment?)
The force on the spanner causes a turning effect or moment on the nut. A larger force would mean a larger moment
What happens if you use a longer spanner (same force as smaller spanner but different distance) ?
Exerts a larger moment because the distance from the pivot is greater
What do you need to do to get the maximum moment?
Push at right angles to the spanner
Why cant you push at any other angles?
It means a smaller moment because the perpendicular distance between the line of action and the pivot is smaller
Where does the centre of gravity hang directly below?
The point of suspension
What is the centre of gravity of an object?
The point at which the weight of the body acts
When will a freely suspended object stop swinging?
When it is vertically below the point of suspension - no moment as the pivot is in line with the line of action of the force
Describe how you can find the centre of gravity of any flat shape using a plumb line
1) Suspend the shape and a plumb line from the same point and wait to until they stop moving
2) Draw a line along the plumb line
3) Do the same again but suspend shade from different pivot point
4) The centre of gravity is where the two lines meet
How can you work out the centre of gravity for simple shapes eg a square?
Look at the lines of symmetry (where two lines cross in the middle is the c.og)
What is the principle of moments?
Total anticlockwise moments = Total clockwise moments
When acting in a balanced object
*Why do you ignore the weight of a seesaw when working out a question?
Its centre of mass is on the pivot, so it does have a turning effect
If a light rod (when you ignore weight in the calculations) is being supported at both ends, will the upwards force be the same?
No - if a heavy object is placed on the rod, the support closest to the object will provide a larger force
If the total anticlockwise moments do not equal the total clockwise moments, what will there be?
A resultant moment - so the object will turn!
