Module 3 - Motion with non-uniform acceleration

Question 1

What is meant by the force: Drag

Answer 1

The frictional force experienced by an object travelling through a fluid, which opposes its motion

Question 2

What are the factors that affect drag travelling through air

Answer 2

1. The speed of the object
2. the shape of the object (streamliness)
3. The texture of the object (roughness)
4. The density of the fluid through which the object travels

Question 3

What are the 2 most important factors that affect the drag of an object

Answer 3

1. The speed of the object
2. The cross-sectional area of the object

Question 4

What are the proportionality of drag with speed and cross-sectional area

Answer 4

Drag α Speed²
- More Frequent Collisions – As speed increases, the object collides with more air molecules per second, increasing resistance.
Higher Impact Force – Each collision with air molecules happens at a higher speed, transferring more momentum and increasing drag.

Drag α Cross-Sectional Area
- This is because there is more surface for collision – A larger cross-sectional area means more air molecules collide with the object, increasing resistance.

Question 5

When an object is just dropped what is the acceleration and why

Answer 5

• Initial acceleration = 9.81m/s/s, this is because the only force acting on the object is its weight.

Question 6

Why does the drag of an object stop increasing when it reaches terminal velocity

Answer 6

Drag α Speed²
- This means that as speed increases, drag increase
- At terminal velocity, velocity is the highest, because there is no resultant force and so no acceleration meaning that the velocity stays constant

Question 7

Explain what is meant by terminal velocity

Answer 7

The maximum velocity reached by an object in free-fall when the weight is equal in magnitude to the drag it experiences

Question 8

Describe what happens to both the velocity and the drag force as an object is dropped in free fall before it reaches terminal velocity

Answer 8

The velocity of the object increases due to it initially accelerating, this means the drag also increases as it increases with the square of speed

Question 9

Describe what happens to the weight of the object and the net force acting on it

Answer 9

• The weight of the object remains constant
• The net Force decreases because F = mg - Drag, and drag is increasing

Question 10

Describe what happens when the drag balances the weight

Answer 10

• The net force is 0, meaning the object will stop accelerating and the velocity will be at its maximum and will be constant –> Terminal Velocity

Question 11

Describe the setup to find the terminal velocity of a ball bearing in a viscous liquid

Answer 11

1. Fill a measuring cylinder and fill it with viscous liquid

Question 12

Describe the methodology to find the terminal velocity of a ball bearing in a viscous liquid

Answer 12

1. Hold a bearing over the liquid and drop it from rest
2. At the same time of the release, start a timer
3. Mark the position of the ball bearing in the tube in regular time intervals
4. Calculate the velocity for the different time intervals and plot a vt graph
5. the terminal velocity is when the velocity is constant

Question 13

What is meant by viscosity

Answer 13

a measure of a fluid’s resistance to flow