Materials - Moments or Torques

Question 1

Moments or Torques
(What is a moment?)
(What does a moment depend on?)
(What is the unit of a torque?)
(What happens if there is an unbalanced torque on a body?)

Answer 1

• A moment of a force, or a torque, is a measure of a force’s tendency to cause a body to rotate.
• a moment depends on the strength of the force, as well as where it acts from.
• The unit of torque is a newton-meter, Nm.
• if there is an unbalanced torque on a body, it will gain rotational acceleration, as there will be a force acting on it in the direction of the torque.

Question 2

Perpendicular Force
(What does Newton’s second law of motion tell us?)
(How is Newton’s second law of motion used in moments and torques?)

Answer 2

• Newton’s second law of Motion tells us that if a force acts on an object, the object will accelerate in the direction of the force.
• This is used in Moments and Torques as if the forces acting on an object are unbalanced, the object will start to move in the direction of a force.

Question 3

Non-perpendicular force
(what is the third angle which needs to be included to calculate the torque?)
(what is the new equation to find the torque of an object?)

Answer 3

• With non-perpendicular forces you need to include a third variable to calculate the torque of an object, this being the angle at which the force is being applied.
• This leads to the equation of torque being F * d * sinθ, where F is the force acting on the object, d is the distance from the pivot and θ is the angle at which the force is acting.

Question 4

Adding Moments.

How do you add resultant forces together to find the one overall force?

Answer 4

• In some cases involving moments and torques, objects will not have just one force acting on them in one direction, this can lead to you having to subtract or add moments.
• to do this you would first calculate the moments of all the forces acting on the object, sort them into the direction they are going, and decide if they need to be subtracted or added together.

Question 5

Torque as a Vector

Can torques be positive or negative?

Answer 5

• In the past cases written about, torques have been treated as a scalar force.
• This is not the case, as you always need to bear in mind which direction the force is acting
• Because of this you can end up with negative torques as well as positive torques, depending on the direction.

Question 6

No fixed point
(What set of forces is the motion of an object which is free to move consist of?)
(what needs to be considered when calculating the rotational part of the motion?)

Answer 6

When a body is free to move, i.e. not fixed at any point, then its motion under a set of forces consists of:
• a linear acceleration according to Newton’s second law, and
• a rotation about its centre of mass.
The rotational part of the motion can be calculated by considering moments about the centre of mass.