Module 3 Pressure Density Archimedes

Question 1

Definition for density?

Answer 1

mass per unit volume

Question 2

What kind of quantity is density, vector or scalar?

Answer 2

scalar

Question 3

What is the symbol for density?

Answer 3

ρ - rho

Question 4

If force given at an angle to the a surface, what must be done before pressure can be calculated?

Answer 4

resolve force to give the component normal to the surface

Question 5

Units for pressure?

Answer 5

pascals, Pa

Question 6

Definition of a pascal?

Answer 6

1 Newton per metre squared

Question 7

To find the maximum pressure that can be exerted by an object what do you do?

Answer 7

weight/smallest area

Question 8

Derive P=ρhg from the formula for volume and pressure

Answer 8

V=Axh (areaheight)
ρ=m/V therefore m = ρV
By combining the two above equations we get m = ρAh
Weight = mg = ρAhg = F
To get P divide both sides by A
Area cancels out to give P=ρhg

Question 9

Explain which equations you need to combine to derive P=ρhg from the formula for volume and pressure

Answer 9

V=Axh
ρ=m/V
Combine arrange for mass
weight(F) = mg
P=F/A

Question 10

What does homogeneity mean?

Answer 10

two quantities have the same units (not necessarily base/SI units)

Question 11

State the Archimedes principle

Answer 11

For an object fully or partially submerged in a fluid, the upthrust is equal to the weight of the fluid displaced

Question 12

For an object traveling upwards in water, what are the forces acting on it?

Answer 12

Upthrust, weight and drag

Question 13

For an object in water, when is terminal velocity reached?

Answer 13

when W+D=U if the object is travelling upwards

when W = U+D if the object is travelling downwards

Question 14

When an object is floating what can be said about the forces acting on it?

Answer 14

W=U, as object is not moving there is no drag

Question 15

Assuming a large depth, explain what happens to a ball who’s weight is<upthrust in water over time if released from the bottom?

Answer 15

Resultant force is upwards
As velocity increases so does drag so resultant force decreases
Acceleration decreases
Eventually terminal velocity is reached when W+D=U

Question 16

Archimedes principle:
For an object fully or partially __________ in a fluid, the upthrust is equal to the ________________

Answer 16

For an object fully or partially submerged in a fluid, the upthrust is equal to the weight of the fluid displaced