Module 3.2 - Forces In Action

Question 1

Four fundamental types of forces

Answer 1

Gravitational
Electromagnetic
Strong nuclear
Weak nuclear

Question 2

Gravitational force

Answer 2

Acts on objects with mass
Infinite range
Weakest strength

Question 3

Electromagnetic force

Answer 3

Acts on objects with charge
Infinite range
Strong

Question 4

Strong nuclear force

Answer 4

Acts on quarks
Tiny range (10^-15m)
Strongest

Question 5

Weak nuclear force

Answer 5

Responsible for radioactive decay
Smallest range (10^-18m)
Weak

Question 6

Define the Newton

Answer 6

The force that causes a mass of 1kg to have an acceleration of 1ms^2

Question 7

Define the resultant force

Answer 7

The sum of all the forces acting on a body

Question 8

Define equilibrium

Answer 8

No resultant force

Question 9

Define terminal velocity

Answer 9

The highest velocity reached by an object in free fall

No longer accelerating

Question 10

Define couple

Answer 10

When two forces have the same magnitude, are opposite in direction, but don’t act through the same line of action

Question 11

Define torque

Answer 11

One of the forces in a couple multiplies by the distance between them

Question 12

Define the moment of a force

Answer 12

The turning effect of a single force

Question 13

State the principle of moments

Answer 13

For a body in rotational equilibrium the sum of the clockwise moments equals the sum of the anticlockwise moments

Question 14

State Archimedes Principle

Answer 14

The upthrust acting on an object immersed in a fluid is equal to the weight of the fluid it has displaced

Question 15

Define the centre of gravity

Answer 15

The point at which the entire weight of an object is considered to act from (i.e. as a single force)

Question 16

How are some objects more stable than others?

Answer 16

Objects with a low centre of gravity and a wide base are more stable than object with a high centre of gravity and a narrow base

Question 17

Describe an experiment to determine an object’s centre of gravity

Answer 17

Hang the object from a clamp stand using string.
From the same hole create a plumb line using a bung and another length of string.
Draw a line along the string across the object.
Repeat this from several points around the object, and where they intersect is the centre of gravity.

Question 18

Describe an experiment to measure the terminal velocity of a body falling through a fluid

Answer 18

Drop a ball bearing into the liquid (e.g. wallpaper paste, heavy oil, liquid detergent) and start a timer as you do so
At given time periods use elastic bands to mark the vertical position of the ball in the column
Once the ball bearing is at the bottom, measure the distance between each consecutive pair of elastic bands
Use a magnet to remove the ball from the tube and repeat
Calculate the average velocity of the ball by dividing each distance between bands by the chosen time period and find the average
Plot a graph of v against cumulative time and draw a smooth curve
Use the graph to identify when the ball reached terminal velocity

Question 19

Define the centre of mass

Answer 19

The single point of an object at which all of its mass can be assumed to be situated

Question 20

How do objects become unstable?

Answer 20

When the object is tilted so the centre of mass lies outside the base width

Question 21

What is meant by neutral stability?

Answer 21

Objects that roll (e.g. ball) have neutral stability as their centre of mass can never fall outside of their base width

Question 22

Define density

Answer 22

Mass per unit volume

Question 23

How do you calculate the density of an irregular shaped object?

Answer 23

Measure the mass of the object using a mass balance
Carefully lower the object into a displacement can containing water
The volume of water displaced is equal to the volume of the object
Use the formula to calculate the density

Question 24

Define pressure

Answer 24

Force per unit area at the normal/right angle to the area

Question 25

When is pressure highest?

Answer 25

When the force exerted is large

When the surface area over which the force acts is small

Question 26

Why does pressure increase with depth in a fluid?

Answer 26

Because of the force exerted by the increased weight of the fluid above

Question 27

Formula for upthrust

Answer 27

Area x pressure (hpg)