The Turning Effect Of Forces

Question 1

How do you work out a moment?

Answer 1

Moment of a force = force (F) x perpendicular distance from pivot (d)
Nm = N x m

Question 2

When will an object balance?

Answer 2

sum of anticlockwise moments = sum of clockwise moments

Question 3

What is the centre of gravity of a ruler?

Answer 3

• The point where the whole weight of the ruler appears to act
• This means that the weight force acts at this point
• Centre of gravity sometimes called centre of mass

Question 4

Describe what happens as a boy stands on a beam

Answer 4

1. The beam is not moving so the upward and downward forces must be balanced
2. The boy is standing in the middle of the beam so the upward forces on the ends of the beam are the same as each other
3. The forces on the ends of a beam depend on where the load is applied
4. Therefore the upward forces on a light beam, supported at its ends, vary with the position of a having object placed on the beam

Question 5

What happens if the boy moves on the beam?

Answer 5

1. If the boy moves right to one end of the beam, then the upward force will all be at that end of the beam
2. As he moves along the beam, the upward forces at the ends of the beam change

Question 6

How do you get the maximum moment or turning effect?

Answer 6

• To push a right angles (perpendicular) to the spanner
• Pushing at any other angle means a smaller moment because the perpendicular distance between the line of action and the pivot is smaller

Question 7

Where does the centre of gravity hang?

Answer 7

• Directly below the point of suspension
• The centre of gravity of an object is the point through which the weight of a body acts
• A freely suspended object will swing until its centre of gravity is vertically below the point of suspension

Question 8

How do you work out the centre of gravity of any flat shape?

Answer 8

1. Suspend the shape and a plumb line from the same point, and wait until they stop moving
2. Draw a line along the plumb line
3. Do the same thing again, but suspend the shape from a different pivot point
4. The centre of gravity is where your two line cross

Question 9

How do you find the centre of gravity for simple shapes?

Answer 9

• Where lines of symmetry meet

- Where the axes of symmetry cross

Question 10

What happens when the moments are not equal?

Answer 10

If the total anti-clockwise moments do not equal the total clockwise moments, there will be a resultant moment (so the object will turn)

Question 11

Where does the weight of a body act through?

Answer 11

Its centre of gravity (draw arrows from centre)

Question 12

What is weight? What is gravity? What is mass?

Answer 12

• Weight is caused by the pull of gravity
• Mass is the amount of stuff it an object, for any given object this will have the same value anywhere in the universe
• Gravity is the force of attraction between all masses

Question 13

What do the upward forces on a light beam, supported at its end vary?

Answer 13

With the position of a heavy object placed on the beam