8.3 Terminal speed

Question 1

Define drag force

Answer 1

the force of fluid resistance on an object moving through the fluid

Question 2

What 3 factors does drag force depend on?

Answer 2

1. the shape of the object
2. its speed
3. the viscosity of the fluid, which is a measure of how easily the fluid flows past a surface

Question 3

Define terminal speed

Answer 3

the maximum speed reached by an object when the drag force on it is equal and opposite to the force causing the motion of the object

Question 4

Describe the motion of an object falling in a fluid

Answer 4

• speed of object released from rest in a fluid increase as it falls
• drag force on it, due to the fluid, increases
• (the resultant force on the object is the difference between the force of gravity on it (its weight) and the drag force)
• as the drag force increases, the resultant force decreases, so the acceleration becomes less as it falls
• if it continues falling, it attains TERMINAL SPEED, when the drag force on it is equal and opposite to its weight
• its acceleration is then 0 and its speed remains constant as it falls

Question 5

Define motive force

Answer 5

the force that drives a vehicle