Module 3.2 - Forces In Action Flashcards
Four fundamental types of forces
Gravitational
Electromagnetic
Strong nuclear
Weak nuclear
Gravitational force
Acts on objects with mass
Infinite range
Weakest strength
Electromagnetic force
Acts on objects with charge
Infinite range
Strong
Strong nuclear force
Acts on quarks
Tiny range (10^-15m)
Strongest
Weak nuclear force
Responsible for radioactive decay
Smallest range (10^-18m)
Weak
Define the Newton
The force that causes a mass of 1kg to have an acceleration of 1ms^2
Define the resultant force
The sum of all the forces acting on a body
Define equilibrium
No resultant force
Define terminal velocity
The highest velocity reached by an object in free fall
No longer accelerating
Define couple
When two forces have the same magnitude, are opposite in direction, but don’t act through the same line of action
Define torque
One of the forces in a couple multiplies by the distance between them
Define the moment of a force
The turning effect of a single force
State the principle of moments
For a body in rotational equilibrium the sum of the clockwise moments equals the sum of the anticlockwise moments
State Archimedes Principle
The upthrust acting on an object immersed in a fluid is equal to the weight of the fluid it has displaced
Define the centre of gravity
The point at which the entire weight of an object is considered to act from (i.e. as a single force)
How are some objects more stable than others?
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
Describe an experiment to determine an object’s centre of gravity
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.
Describe an experiment to measure the terminal velocity of a body falling through a fluid
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
Define the centre of mass
The single point of an object at which all of its mass can be assumed to be situated
How do objects become unstable?
When the object is tilted so the centre of mass lies outside the base width
What is meant by neutral stability?
Objects that roll (e.g. ball) have neutral stability as their centre of mass can never fall outside of their base width
Define density
Mass per unit volume
How do you calculate the density of an irregular shaped object?
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
Define pressure
Force per unit area at the normal/right angle to the area
When is pressure highest?
When the force exerted is large
When the surface area over which the force acts is small
Why does pressure increase with depth in a fluid?
Because of the force exerted by the increased weight of the fluid above
Formula for upthrust
Area x pressure (hpg)
