3.2 Forces In Action

Question 1

What is the centre of mass of an object?

Answer 1

The point at which the weight can be assumed to act.

Question 2

What does the weight of an object depend on?

Answer 2

It’s mass and the gravitational field strength (W=mg)

Question 3

What is a free-body diagram?

Answer 3

It is a diagram showing the set of forces acting on a single object

Question 4

What is weight?

Answer 4

The force due to gravity that acts through an object’s centre of mass

Question 5

What is friction?

Answer 5

The force that acts between two surfaces in contact to oppose motion

Question 6

What is drag?

Answer 6

The resistive force that acts on an object moving through a fluid

Question 7

What is tension?

Answer 7

The force within a stretched object such as a cable or rope

Question 8

Upthrust

Answer 8

The upward buoyant force that acts on an object in a fluid.

Question 9

Normal contact force

Answer 9

A force that acts perpendicular to a surface when an object rests on it.

Question 10

How do you calculate the component of weight down a slope?

Answer 10

W sin (θ) where θ is the angle between the slope and horizontal

Question 11

How do you calculate the component of weight acting perpendicular to a slope?

Answer 11

W cos (θ) where θ is the angle between the slope and horizontal

Question 12

What are the key factors in determining the magnitude of drag force acting on an object in a fluid?

Answer 12

Speed and cross-sectional area

Question 13

Terminal velocity

Answer 13

The maximum speed reached by a falling object when drag and weight are equal.

Question 14

What is a moment?

Answer 14

The turning effect produced by a force.

Question 15

Units for moment

Answer 15

Nm

Question 16

How do you calculate a moment about a point?

Answer 16

Force x perpendicular distance to the line of action of the force

Question 17

What is meant by a body being in equilibrium?

Answer 17

The net force and the net moment acting on the body are both zero.

Question 18

What is the principle of moments?

Answer 18

For an object in rotational equilibrium the sum of the clockwise moments about any point is equal to the sum of anticlockwise moments about that point.

Question 19

What is a couple?

Answer 19

A pair of equal and opposite forces acting on an object with different lines of action.

Question 20

How do you calculate the moment of a couple?

Answer 20

Force x perpendicular distance between the lines of action of the forces.

Question 21

What is a triangle of forces?

Answer 21

A vector diagram of the three forces acting on an object in equilibrium

Question 22

What is a resultant/ net force?

Answer 22

The vector sum of forces acting on an object

Question 23

What is the density of a substance?

Answer 23

Mass per unit volume

Question 24

What are the units for density?

Answer 24

kgm^-3

Question 25

What is pressure?

Answer 25

Normal force acting per unit area

Question 26

What is Archimedes principle?

Answer 26

The upthrust exerted on a body immersed in fluid, whether partially or fully submerged, is equal to the weight of the fluid that the body displaces.

Question 27

What is p in the equation p = hρg

Answer 27

Pressure exerted by a fluid

Question 28

What is ρ in the equation p = hρg

Answer 28

Density of the fluid

Question 29

What is h in the equation p = hρg

Answer 29

Depth of the fluid