6 Forces in Equilibrium

Question 1

What is a vector?

Answer 1

any physical quantity that has a direction as well as a magnitude

Question 2

what is a scalar?

Answer 2

any physical quantity that is not directional

Question 3

What is displacement?

Answer 3

distance in a given direction

Question 4

what is velocity?

Answer 4

speed in a given direction

Question 5

what is the resultant force of multiple forces?

Answer 5

the combined effect of multiple forces

Question 6

How do you find the magnitude and angle of a resultant force?

Answer 6

• magnitude - Pythagoras
• angle - trig

Question 7

What does resolving a force mean?

Answer 7

splitting a force F into two perpendicular components

Question 8

What does equilibrium mean?

Answer 8

when the forces acting on an object are balanced so it is at rest or in uniform motion

Question 9

How do you check if an object is in equilibrium if three forces are acting on it?

Answer 9

• resolve each force along the vertical and horizontal lines
• balance the components along each line

Question 10

What is a moment?

Answer 10

the moment of a force about any point is defined as the force x perpendicular distance from the line of action of the force

Question 11

what is the principle of moments?

Answer 11

for an object in equilibrium, the sum of the clockwise moments about any point = the sum of the anticlockwise moments about that point

Question 12

what is the centre of mass of a body?

Answer 12

the point through which a single force on the body has no turning effect

Question 13

what is a support force?

Answer 13

When an object is in equilibrium, there is a force equal and opposite to the total downwards force

Question 14

how do you work out support forces with two supports?

Answer 14

use the moments about each point

Question 15

what is a couple?

Answer 15

a pair of equal and opposite forces acting on a body but not along the same line

Question 16

what is the formula for the moment of a couple?

Answer 16

force x perpendicular distance between the lines of action of the forces

Question 17

what is stable equilibrium?

Answer 17

when a body returns to its equilibrium position when its displaced then released

Question 18

what is unstable equilibrium?

Answer 18

when a body is displaced and then released, it does not return to its equilibrium position

Question 19

what is tilting?

Answer 19

when an object is acted on by a force which raises it up on one side

Question 20

what do you have to consider when looking if an object is going to tilt?

Answer 20

the moments of the force applied to make it tilt and the moment caused by the weight.

Question 21

when does an object topple?

Answer 21

when it is tilted too far.
this is because as it is tilted more and more, the line of action of the weight passes closer and closer to the pivot and eventually passes beyond the pivot

Question 22

what is a free body diagram?

Answer 22

a diagram which just shows the forces acting on an object

Question 23

what is the triangle of forces?

Answer 23

three forces as vectors acting on an object in equilibrium should make a triangle