Topic 4 Materials

Question 1

For stokes law to be applied what assumptions have to be made?

Answer 1

-Small object.
-Spherical object.
-Moving at low speed.
-Occurs in laminar flow.

Question 2

When the fizzy drink is poured, it contains many spherical bubbles of gas which rise and form the foamy ‘head’ at the top of the drink.

A bubble, initially at rest in the liquid, accelerates until it achieves a uniform upward velocity.

Explain the motion of the bubble. (4)

Answer 2

-Initially upthrust>weight and drag=0.
-Unbalanced forces, so accelerates upwards.
-As velocity increases drag increases.
-Until U=D+W, so resultant force=0 and acceleration=0.

Question 3

A seiche is a standing wave that can form on the surface of a lake in strong winds, causing flooding and erosion. The temperature of the lake decreases with depth.

Explain how this may affect the rate at which a particle falls. (2)

Answer 3

-Viscosity increases with decreasing temperature.
-So rate at which particle falls decreases with depth.