Forces moments and equilibrium

Question 1

How to find the vertical and horizontal components if Force F is diagonal

Answer 1

FV = F sin θ
FH = F cos θ

Question 2

Exam q
In the example opposite the weight of the block W has components parallel, F1 and perpendicular F2 to the inclined plane .
Calculate these components if the block’s weight is 250N and the angle of the plane 20o

Answer 2

F2 = W cos θ = 250 x cos 20o
F2 = component perpendicular to the plane = 235 N

F1 = W sin θ = 250 x sin 20o
F1 = component parallel to the plane = 85.5 N

Question 3

Moment of a force def

Answer 3

Also known as the turning effect of a force.

Question 4

Equation of a moment

Answer 4

force x perpendicular distance from the turning point to the line of action of the force

moment = F x

Question 5

Unit of moment

Answer 5

Nm

Question 6

Moments can a and c

Answer 6

Anticlockwise and clockwise

Question 7

Centre of mass def

Answer 7

The centre of mass of a body is the point through which a single force on the body has no turning effect.

Question 8

How to find the centre of mass?

Answer 8

Step 1: Hang up the irregularly shaped object
2. Suspend the shape from a location near an edge. Drop a plumb line and mark on the object.
3. Suspend the shape from another location not too close to the first. Drop a plumb line again and mark its position.

Question 9

Principle of moments

Answer 9

When an object is in equilibrium (e.g. balanced):

the sum of the anticlockwise moments = the sum of the clockwise moments
F1 x1 = F2 x2

Question 10

How to know if a body is at equilibrium?

Answer 10

When a body is in equilibrium it will EITHER be at rest OR move with a constant linear and rotational velocity.

Question 11

Conditions required for equilibrium

Answer 11

1.The resultant force acting on the body must be zero.

2.The principle of moments must apply about any point on the body. In other words the resultant moment is zero.

Question 12

For a system to be at equilibrium it must have (talk about forces as well)

Answer 12

For a system to be in equilibrium, the sum of the moments must equal zero and the sum of the forces must equal zero. Consider the following scenarios and solve using the principle of moments:

Question 13

What is a couple?

Answer 13

A couple is a pair of equal and opposite forces acting on a body, but not along the same line.

Question 14

What is a torque?

Answer 14

Torque is another name for the total moment of a couple

Question 15

Torque equation

Answer 15

F x d