Module 3: Chapter 4 - Forces in Action Flashcards
What are the 8 stores of energy?
- Thermal
- Kinetic
- Nuclear
- Elastic Potential
- Gravitational Potential
- Chemical Potential
- Magnetic
- Electrostatic
What are the 4 energy transfer pathways?
- Heating
- Radiation (Light, Sound, Nuclear)
- Electrical Work
- Mechanical Work
What are the 2 different types of forces?
Contact and non-contact forces
What are 8 examples of contact forces?
- Drag (Friction, air + water resistance)
- Tension
- Compression
- Upthrust
- Torsion
- Thrust
- Lift
- Normal Contact Force
What are 3 examples of non-contact forces?
- Weight (Gravitional pull)
- Electrostatic push/pull
- Magnetic push/pull
What are the 4 fundamental forces?
- Gravitational Force
- Electromagnetic/electrostatic force
- Weak Nuclear Force
- Strong Nuclear Force
What does the gravitational force act upon?
Anything with mass
What does electrostatic/electromagnetic force act upon?
Anything with charge
What is a scalar force?
A force which has magnitude only
What is a vector force?
A force which has magnitude and a direction
What is common between all forces?
- They are a push or a pull
- They are measured in Newtons
- They are vectors
- They always act in pairs
What can a force do to an object?
- Change the motion of the object
- Change the direction of the object
- Change the shape of the object
What is Newton’s third law of motion?
For every action there is an equal and opposite reaction
What happens if the result force acting on an object is 0?
The forces are balanced, therefore the object will continue in uniform motion, if it is at rest it will remain at rest and if it is in motioin in will move at a constant velocity
What happens if the result force acting on an object is not 0?
The forces are unbalanced, therefore the object will start moving, accelerate, or decelerate
What is θ
NOT CONFIRMED
32*
NOT CONFIRMED
What is a moment?
The turning effect of a force which acts around a pivot
What is the equation for a moment?
Moment = Force x Perpendicular Distance to the line of action of the force
What are the units for Moment?
Nm
What is the principle of moments?
If a body is in equilibrium, the sum of the clockwise moments is equal to the sum of the anti-clockwise moments
A 200N 3m long plank hangs over the edge of a cliff by 1m. How far can a man of 800N walk on the plank over the edge of the cliff before the plank tips over?
0.125m
Calculate the moment
27.5Nm anticlockwise
Calculate W
6.67N
What is a couple?
2 equal and opposite forces (parallel forces) acting upon a body but on different lines of action
What is stable equilibrium?
If a body is displaced from the equilibrium position then released, it will return to the equilibrium position
What is unstable equilibrium?
If a body is displaced from the equilibrium position then released, it will not return to the equilibrium position
What is neutral equilibrium?
A system is in neutral equilibrium if its equilibrium is independent of displacements from its original position
What are the 3 types of stability equilibrium?
Stable, Usntable, Neutral
What does stability depend on?
- Width of base
- Height of centre of mass
What causes an object to topple?
If the line of action of the object’s weight does not pass through the base of the object then the object will topple
What is triangle of forces used for?
To consider 3 forces acting in equilibrium
What is the centre of gravity of an object?
Weight is caused by the attraction of every atom inside an object to another body. The sum of all these forces appear to act from a single point for any object, this is the centre of gravity
What is the centre of mass of an object?
The point at which a single force on a body has no turning effect (the point in an object where the mass can be throught as being concentrated)
How do you find the centre of mass in a symmetrical object?
divide the object by the lines of symmetry
How do you find the centre of mass in an irregular object?
A freely suspended object will always come to rest with its centre of gravity vertically below the point of suspension:
1. Make a hole in the material and hang from a clamp and stand
2. Hang a piece of string from it with a weight (plumb-bob) on the end so you can trace the plumb line
3. Make another hole in a different place and do the same thing
4. Where they cross is the centre of mass of the object
If an object is suspended from 2 different strings, how can you calculate the tension in each string?
- Sketch the triangle of forces
- Calculate the tension in each string using trigonometry
An object in equilibrium is being acted on by 3 different forces, if you know 2 forces, how can you find the third?
Arrange the 3 vector forces into a triangle and use trigonometry
What is important when drawing a triangle of forces?
- The forces must be joined head to tail, you must be able to follow the traingle round in 1 direction
- They must be in the direction shown in the original diagram
- Include all angles
draw the triangle of forces
.
What is the equation for the vertical component of each tension when an object is suspended from 2 cables?
Tv₁ = T₁Cos(θ₁)
Tv₂ = T₂Cos(θ₂)
Tv₁ + Tv₂ = Weight
What is the equation for the horizontal component of each tension when an object is suspended from 2 cables?
Tₕ₁ = Tₕ₂
What is density?
The mass per unit volume
What is the equation for density?
Density = mass / volume
ρ = m / v
What are the units for density?
kg m⁻³
What is the density of water?
1000 kg m⁻³
What is archimedes’ principle?
The upthrust on an object in a fluid is equal to the weight of the fluid displaced
Upthrust = weight of fluid displaced
What is the equation for upthrust?
Upthrust = Vρg
V = volume of the fluid displaced, ρ = density of fluid displaced
When will an object float?
If the density of the object is less than that of the fluid, it will float
What properties affect upthrust?
- Volume of fluid displaced
- Density of fluid
- Gravitational field strength
What is the equation for pressure in a fluid?
Pressure = height x density x gravitational field strength
P=hρg
What is a barometer?
A device that can be used to measure atmospheric pressure depending on the changing height of a column of fluid
What is a manometer?
A U-shaped device that can be used to measure the pressure difference between 2 pressures of interest
What is newtons second law of motion?
F = ma
A net (resultant) force acting upon an object will cause it to accelerate
What is weight?
The gravitational force acting on an object through its centre of mass
What is friction?
The force that arises when 2 objects in contact move past each other
What is drag?
The resistive force on an object travelling through a fluid
What is tension?
The force within a stretched cable or rope
What is upthrust?
An upward buoyancy force acting on an object partially or completely submerged in a fluid
What is normal contact force?
A force arising when one object rests against another object
What factors affect the magnitude of a drag force?
- Speed
- Cross sectional area
- density of fluid
drag ∝ speed²
What is the equation for the acceleration of an object in freefall?
a = (mg - D)/m
acceleration = net force / mass
D = drag
What is the purpose of a couple?
To produce rotational motion with no translational motion
What is torque?
The moment of a couple (a force that causes rotation)
What is the equation for torque of a couple?
Torque of a couple = one of the forces x perpendicular separation between the 2 forces
What is a fluid?
A substance that can flow
What causes upthrust?
The difference in pressure between the top surface and bottom surface of an object
How can you determine what fraction of an object will be submerged in a liquid?
Volume submerged / Total volume = density of object / density of fluid
According to a student, Weight = Normal contact force, is a result of Newton’s third law of motion. Explain whether they are correct
The student is incorrect as weight and normal contact force are not the same type of force. Therefore they cannot be a product of Newton’s third law as they are of different types
