3.2 Forces In Action Flashcards
Newton’s second law.
F= ma
What are the four fundamental forces of nature?
- gravitational force
- electromagnetic force
- weak interaction
- strong interaction
Which is the weakest of the four fundamental forces?
Gravitational
What does the electromagnetic force do?
Holds atoms and molecules together.
How can the electromagnetic force be described?
The exchange of photons between charged particles of magnetic materials.
What is the weak interaction responsible for?
Radioactive decay.
What is the range of the weak interaction?
10-18m
What is the strong interaction responsible for?
Holding subatomic particles together.
What is the strongest fundamental force of nature?
The strong interaction.
What is the range of the strong interaction?
10-15m
What are the five main types of force we need to know about?
Tension, normal contact force, upthrust, friction and drag.
What is the equation for tension?
Tension = mass x acceleration.
What is upthrust?
The upwards force that a liquid or gas exerts on a body floating in it due to the water displaced.
When will an object move at terminal velocity?
When the magnitude of the body’s weight becomes equal to the sum of the drag and the upthrust and the resultant force is 0.
What is a fluid?
A liquid or a gas.
What is p in the equation for drag?
The density of the fluid.
What is A in the equation for drag?
The cross sectional area of the moving object
What is v in the equation for drag?
Velocity of moving object.
What is equilibrium?
When all the Coplanar forces are balanced.
How can we work out the resultant of two forces acting on a body?
- a scale drawing
- right angled vector triangle.
What does a triangle of forces represent?
The direction and magnitude of three coplanar forces that are acting on an object in equilibrium.
Equation for turning moment?
Magnitude of force (N) x perpendicular distance from a fixed point (m)
Unit of turning moment?
N m
Define moment of force or turning moment.
The product of the and perpendicular distance of its kind of action from the point or axis.
What is the fancy name of the pivot?
Fulcrum
Define the principle of moments.
For an object to in rotational equilibrium, the sum of the clockwise moments about a point must be the sum of the anti-clockwise moment about the same point.
What are the two conditions for equilibrium?
1) resultant force on the objects must be 0
2) sum of clockwise = sum of anti-clockwise
What is drag?
Friction force experienced by an object travelling through a fluid.
What is Archimedes principle?
A law stating that a body totally or partially immersed in a fluid is subject to an upward force equal in magnitude to the weight of fluid it displaces.
When does a couple occur?
When two equal, antiparallel forces act to produce rotation - no linear motion occurs.
What is a torque?
The moment or turning effect of a couple
The product of one of the forces and the perpendicular distance between them
What are the units of turning moment (torque)?
N m
How do you calculate the turning moment produced by a couple?
One of the forces multiplied by their separation.
What factors affect drag?
Cross sectional area
The density of the fluid
What is the centre of mass?
The single point at which all of the mass of the object can be assumed to be situated.
What happens if a forces acts directly on the centre of mass?
Move in a straight line.
What happens if a force does not act on the centre of mass?
Move with an added rotational motion.
What is the centre of gravity?
Single point through which the entire weight of the object can be thought to act.
Define the Newton.
Force is 1N when 1kg of mass has an acceleration of 1ms-2
Equation relating velocity and drag
Fd=kv^2
Equation for pressure
Hpg
