1)The turning effect of a force is called the …….. …. of the force ( 1 mark)

2) Give two ways in which you can increase the spanner’s turning effect. ( 2 marks)

April 18, 2023

3) Calculate the spanner’s turning effect in newton metres. (2 marks)

1)The turning effect of a force is called the ..momentun …. of the force ( 1 mark)2) Give two ways in which you can increase the spanner’s turning effect. ( 2 marks)

• use a longer spanner (1 mark)

• use a greater force / pull (1 mark)

April 18, 2023

April 18, 2023

3) Calculate the spanner’s turning effect in newton metres. (2 marks)

Moment = 20 N x 0.20m (1 mark)

Moment = 4 Nm (1mark)

Centre of Mass and stability

L.O.: Find out the centre of mass of

an object Explain how the stability on an

object may be increased.

April 18, 2023

Homework: any pending questions from workbook pages 104-106

April 18, 2023

CENTRE OF MASS

The centre of mass of an object is the point where its mass may be thought to be concentrated.

April 18, 2023

• How to find the centre of mass.

a)For symmetrical objects, its centre of mass is along the axis of symmetry. If the object has more than one axis of symmetry, its centre of mass is where the axes of symmetry meet.

April 18, 2023

• How to find the centre of mass.

b)When a suspended object is in equilibrium, its centre of mass is directly beneath the point of suspension.

April 18, 2023

• Tasks:

• 1) workbook page 104, Q3• 2) workbook page 105, Q4-6

April 18, 2023

Q6a)

Hang the plumb line from the same point as the piece of card. Draw a pencil line on the card along the plumb line

Hang the card in a different position and do the same thing again. Where the two lines cross is the centre of mass.

April 18, 2023

• Q6b)

Repeat the same steps for several pivot points to get multiple lines that will all cross at the centre of mass.

April 18, 2023

April 18, 2023

1)Calculate the moment of the girl (2 marks)

360 (Nm) 1)What must her father do to

increase his moment? (1 mark)

• move to(wards) the left / to(wards) the / his end 1 • or move away from the centre / pivot / axis (of

rotation) or move away from the girl / the child / his daught

April 18, 2023

Stability

L.O.:Explain how the stability on an

object may be increased.

April 18, 2023

• What factors affect the stability of an object?

April 18, 2023

April 18, 2023Stability applet

April 18, 2023Stability

stable falls over

• An object will tend to topple over if the line of actions of its weight is outside its base.

April 18, 2023Toppling bus

April 18, 2023CoG wedge

•The point on an object where all its weight seems to be concentrated is called the centre of mass.

weight of wedge

contact force of pivot

April 18, 2023Stable

•If the wedge is slightly moved it will return to its original position.

•The wedge is said to be in stable equilibrium.

April 18, 2023Stable

•If the wedge is slightly moved it will return to its original position.

•The wedge is said to be in stable equilibrium.

April 18, 2023Stable bottle

April 18, 2023Unstable

•If the wedge is slightly moved it will topple over.

•The wedge is said to be in unstable equilibrium.

April 18, 2023Unstable

•If the wedge is slightly moved it will topple over.

•The wedge is said to be in unstable equilibrium.

April 18, 2023Unstable bottle

April 18, 2023Neutral stability

•If the cylinder is slightly moved it will return stay in its new position.

•The cylinder is in neutral equilibrium.

April 18, 2023Neutral stability

•If the cylinder is slightly moved it will return stay in its new position.

•The cylinder is in neutral equilibrium.

April 18, 2023Neutral bottle

• Task

1)Workbook page 106, Q2-42)Workbook page 105, Q6

April 18, 2023

Q4)The weight acts at the centre of mass =40 cm

from the pivot.

The leg is 80- 5= 75 cm from the pivot

Anticlockwise moment = clockwise moment40 N x 0.4 m = F x 0.75 m16Nm = F x 0.75m16/0.75= FF = 21.3 N

April 18, 2023