Chapter 4~forces - Vectors And Moments

Question 1

What is the resultant force?

Answer 1

The combined effect of several forces

Question 2

There are 4 main forces that an object (a car 🚙) experiences when traveling up a hill.

Answer 2

1. Weight (W=mg)
2. The contact force (N) of the road, it’s normal reaction
3. Air resistance D
4. The forward force F caused by friction between the car tyres and the road.

Question 3

If you draw a scale drawing be careful to do 2 things, namely :

Answer 3

1. State the scale being used

2. draw a large diagram to reduce the uncertainty

Question 4

If the object is in equilibrium the resultant force must equal to

Answer 4

Zero

Question 5

If we know an object is in equilibrium so the resultant force equals zero than we can work out the values of one or more….

Answer 5

Unknown forces

Question 6

Equilibrium definition :

Answer 6

°An object in equilibrium is either at rest or traveling with a constant velocity because the resultant force on it is zero 0⃣

Question 7

Definition of triangle of forces

Answer 7

A closed triangle drawn for an object in equilibrium. The sides of the triangle represent the forces in both magnitude and direction

Question 8

NB!!!! On a free body diagram for forces acting on a body on an inclined plane.
Resistance is given.
But what are the components of the other 3 forces acting upon that object?

Answer 8

1. Weight of the object =mg
2. Component of weight down the slope:W= mgsin🎈
3. The reaction force which is the component of weight perpendicular to the plane:

W=mgcos🎈

Question 9

Definition of the centre of gravity

Answer 9

°the centre of gravity of an object is defined as the point where all the weight of the object may be considered to act

Question 10

The quantity which tells us about the turning effect of a force is its…

Answer 10

Moment

Question 11

A moment of a force depends on 2 things :

Answer 11

1. The magnitude of the force (the greater the force, the greater the moment)
2. The perpendicular distance of the force from the pivot (the further the force acts from the pivot, the greater the moment)

Question 12

The moment of a force is defined as :

As well as its formula

Answer 12

°The moment of a force is equivalent to the product of the force and the perpendicular distance of the pivot from the line of action of the force.

Moment of a force = F × perpendicular distance of pivot to F

Question 13

The unit for a moment is

Answer 13

Nm

Question 14

What is the principle of moments?

Answer 14

For any object that is in equilibrium, the sum of the clockwise 🔃 moments about any point provided by the forces acting on the object equals the sum of anticlockwise 🔄 moments about that same point.

Therefore, there is no resultant force

Question 15

Definition of a couple

Answer 15

° a pair of equal and antiparallel forces having a turning effect but no resultant force.

Question 16

A couple has a turning effect but does not cause the object to…

Answer 16

Accelerate

Question 17

To form a couple, the 2 forces must be :

3things

Answer 17

1. Equal in magnitude
2. parallel, but opposite in direction
3. Separated by a distance d

Question 18

Definition of a torque of a couple and unit

Answer 18

°the product of one of the forces of the couple 👫 and the perpendicular force between them.

Unit :Nm

Question 19

Formula for torque of a couple 👫

Answer 19

Torque of a couple 👫

= one of the forces ×distance between the forces

Question 20

For an object to be in equilibrium, 2 conditions must be met at the same time ⌚ :

Answer 20

1. The resultant force acting on the object is zero

2. The resultant moment is zero

Question 21

With a couple the moment of a couple does NOT depend the point about which it acts, it only depends on…

Answer 21

The perpendicular distance between the two forces