5105 NA_Chap 5 Turning Effects of Forces

Chap 5 Turning Effects of Forces

Science Physics 5105

Learning Outcomes

• describe the moment of a force in terms of its turning effect and relate this to everyday examples

• recall and apply the relationship moment of a force (or torque) = force × perpendicular distance from the pivot to new situations or to solve related problems

• state the principle of moments for a body in equilibrium

• apply the principle of moments to new situations or to solve related problems

• show understanding that the weight of a body may be taken as acting at a single point known as its centre of gravity

• describe qualitatively the effect of the position of the centre of gravity on the stability of objects

Multiple Choice

Which diagram best demonstrates the use of the moment of force?

Multiple Choice

The moment of a force causes an object to

• move forward

• move backward

• stop moving

• turn about a fixed point

Multiple Choice

Moment can be calculated using the equation:

• M = F × d

• M = F / d

• M = F² × d

• M = F / d²

Multiple Choice

The turning effect of a force on a door is greater when it is applied at

• A point near the hinges and perpendicular to the door

• A point near the hinges and parallel to the door

• A point far away from the hinges and perpendicular to the door

• A point far away from the hinges and parallel to the door

Multiple Choice

A heavy beam is resting on two supports. There are three forces acting on it.

The beam is in equilibrium.

Which statement is correct?

• All the forces are equal in value.

• The forces are in one direction and their turning effects are in the opposite direction.

• The resultant force is zero and the resultant turning effect is zero.

• The total upward force is twice the total downward force.

Multiple Choice

A see-saw is made by resting a long plank of wood with its centre of gravity on the barrel.

A boy sits on one side of the barrel and a girl sits on the other side so that the see-saw is balanced.

Which of the following statements must be true?

• boy’s weight = girl’s weight

• distance x = distance y

• moments of the girl = moments of the boy

• moment of the girl > moment of the boy

Multiple Choice

Assuming the system is in equilibrium, calculate the missing distance d.

• 3.4 m

• 2.8 m

• 4.4 m

• 1.6 m

Multiple Choice

The beam in the diagram is not balanced.

Which changes balances the beam?

• moving the 2N weight 10 cm to the right

• moving the 5 N weight 10 cm to the right

• replacing the 2N weight with a 7.5 N weight

• replacing the 5N weight with a 3N weight

Multiple Choice

An empty glass is placed on a join between two tabes as shown. The glass remains stable.

Which point is the centre of gravity of the glass?

• A

• B

• C

• D

Multiple Choice

There is a hole in the handle of a hammer so that it can be hung from a nail.

The centre of gravity of the hammer is marked G.

Which hammer is the most unstable?