Unit 1.3 - Dynamics Flashcards
Does an object always follow the path of the largest force?
No - only if its in a straight line
Does a spaceship’s velocity once the thrust has been turned off remain equal?
Yes - there’s no forces in space to change its velocity
What does net force in a direction cause?
Acceleration in that direction
Do faster objects have larger forces on them?
No
What do inanimate objects do?
Exert forces
Is it possible to have no forces on an object?
No
Force
A push or pull acting on a body from an external body - the effect of acceleration
What is the word for a push or pull acting on a body from an external body?
A force
Relationship between acceleration and force
The more a mass accelerates, the bigger the force causing the acceleration
How many fundamental force types are there?
4
What are the four fundamental forces?
Strong
Weak
Electromagnetic
Gravitational
What does the gravitational force apply to?
Anything that has a mass
Which force applies to anything that has a mass?
The gravitational force
What type of force it the gravitational force?
Always an attractive force
Which force takes place when something is pushed?
Electromagnetic
How does the electromagnetic force move an object?
Electrons in the outer shells of the pusher repel the electrons in the outer shell of the pushed
What does the fact that the electrons in the outer shell of the pusher repel the electrons in the outer shell of the pushed mean?
That the electromagnetic force moves objects that are pushed
What type of force can the electromagnetic force be?
An attractive force
Example of the electromagnetic force being an attractive force
Between a positively charged balloon and a negatively charged cloth
What are the two main types of forces that apply in situations?
Constant forces
Action-at-a-distance forces
Name 6 contact forces
Tension
Normal
Air resiatance
Spring
Applied
Fricional
Friction force symbol
Ffriction or Fres
Friction force definition
The force exerted by a surface as an object moves across it/makes an effort to
What is the force exerted by a surface as an object moves across it/makes an effort to?
Frictional force
Which force has at least 2 types and what are they?
Frictional force
Static
Sliding
What are static and sliding forces types of?
The frictional force
What does a frictional force often do?
Opposes the motion of an object
What does the frictional force depend on?
The nature of the two surfaces
The degree they’re pressed together
How does the frictional force result?
From 2 surfaces being pressed together closely, which causes intermolecular forces between molecules of different surfaces
Which type of force often opposes the motion of an object?
The frictional force
Which force depends on he nature of the two surfaces and the degree of which they’re pressed together?
Frictional force
Which force results from 2 surfaces being pressed together closely? How does this happen?
Frictional force
Causes intermolecular attractive forces between molecules of different surfaces
When are intermolecular attractive forces experienced between molecules of different surfaces?
When 2 surfaces are closely pressed together (frictional force)
Tension force symbol
Ftension or T
Which force is T the symbol for?
Tension force
Tension force definition
The force that is transmitted through a string, rope, cable or wire when pulled tight by forces acting on opposite ends
What is the force that is transmitted through a string, rope, cable or wire when pulled tight by forces acting on opposite ends?
Tension force
Where is the tension force directed?
Along the length of the wire
How does the tension force act?
Pulls equally on the objects on the opposite ends of the wire
Which force pulls equally on the objects in the opposite ends of the wire?
The tension force
When does the tension force act?
When pulled tight by forces acting opposite ends
Which force is directed along the length of a wire?
Tension force
Normal force definition
The support force exerted upon an object that is in contact with another stable object
What is the support force exerted upon an object that is in contact with another stable object?
Normal force
Normal force symbol
Fnormal or N
N force meaning
Normal force
What type of objects does the normal force act upon?
Solids
(So it wouldn’t occur on something like a balloon for example)
Applied force definition
Force applied to an object by another person or object
What’s the force applied to an object by another person or object?
Applied force
Applied force symbol
Fapplied or Fthrust or fengine
Fthrust force
Applied force
Fengine force
Applied force
What are the contact forces?
Tension
Normal
Air resistance
Spring
Applied
Frictional
What are the action-at-a-distance forces?
Gravitational (or weight), electrical and magnetic force
Spring force definition
Force exerted by a compressed or stretched spring upon any object attached to it
What is the force exerted by a compressed or stretched spring upon any object attached to it ?
Spring force
Spring force symbol
Fspring
What is directly proportional with most springs (+which ones especially)?
Magnitude of the force and the amount of stretch/compression of the spring
(Those that obey Hooke’s law)
What is the relationship between the magnitude of the force and the amount of stretch/compression of a spring with most springs (+which ones especially)?
Directly proportional
(Those that obey Hooke’s law)
What is an object that compresses or stretches a spring always acted upon by?
A force that restores the object to its rest/equilibrium position
What is a force that restores an object back to its rest/equilibrium position always acting upon?
An object that compresses or stretches a spring
Air resistance force definition
A type of frictional force that acts upon objects as they travel through the air
What type of force is a type of frictional force that acts upon objects as they travel through the air ?
Air resistance force
Air resistance force symbol
Fair resistance or Fdrag
What does the air resistance force often oppose?
The motion of an object
When is the air resistance force most noticeable?
Objects travelling at high speeds
Objects with large surface areas
For objects travelling at high speeds or with large surface areas, what is most noticeable?
The air resistance force
What happens to the air resistance force and why?
Is frequently neglected
-Negligible magnitude
-Mathematically difficult to predict its value
Why is the air resistance force frequently neglected?
-Negligible magnitude
-Mathematically difficult to predict its value
As the air resistance force has negligible magnitude and is mathematically difficult to predict its value, what happens to it frequently?
Is neglected
Other name for the gravitational force
Weight
Other name for the force of weight
Gravitational force
Gravitational force symbol
Fgrav or W
W symbol
Weight
Gravitational force or weight definition
The force with which the earth, moon or other massively large object attracts another object towards itself
What’s the force with which the earth, moon or other massively large object attracts another object towards itself?
Gravitational force or weight
Which force do all objects on earth experience and how?
The force of gravity
Downward, towards the centre of the earth
In which direction do al objects experience the force of gravity?
Downwards, towards the centre of the earth
Magnetic force definition
The force exerted on a magnetic or charged object due to a magnetic field
What’s the force exerted on a magnetic or charged object due to a magnetic field ?
Magnetic force
Electric force definition
The force exerted on a charged object due to an electrical field
What’s the force exerted on a charged object due to an electrical field?
Electrical force
What gives us Newtons laws of motion?
The action of forces on bodies
What do the actions of forces on bodies give us?
Newton’s laws of motion
What do all forces act in?
Newton’s third law pairs (N3)
N3
Newton’s third law pair
What’s the symbol for a Newton’s third law pair?
N3
Can forces exist alone?
No - only as Newton’s third law pairs
What’s different between Newton’s third law pairs?
Different effects
What are the rules for Newton’s third law pairs?
Must act on different bodies
Must be equal and opposite in magnitude
Must be the same type of force
What are…
Must act on different bodies
Must be equal and opposite in magnitude
Must be of the same type of force
…the properties of?
Newton’s third law pairs
What’s the N3 pair for the gravitational force of the Earth pulling on a ball?
An equal and opposite in magnetise gravitational force pulling the Earth towards the ball
When a ball is flying through the air, what is the effect of the force on the ball and what is the effect on the earth?
Effect of the force on the ball : accelerate it towards earth
Effect of the force on the earth : accelerate it towards the ball
If the N3 pair of a ball flying through the air is the gravitational force of the Earth being pulled towards the ball, why don’t we notice the earth moving?
Mass of the ball is much smaller - the acceleration of the ball is more noticeable than the acceleration on earth
What are free body diagrams used for?
To show the relative magnitude and direction of all forces acting upon an objet in a given situation
What is used to show the relative magnitude and direction of all forces acting upon an objet in a given situation?
A free body diagram
What does a free body diagram show all the forces acting upon?
One object
What’s the purpose of a free body diagram?
To make it easier to calculate the effects of forces on an object
What does the size of the arrow show on a free body diagram?
The magnitude of the force
What shows the magnitude of a force on a free body diagram?
The size of the arrow
What does the direction of the arrow show on a free body diagram?
The direction of the force
What shows the direction of the force on a free body diagram?
The direction of the arrow
What do we do to all of the forces on a free body diagram?
Label them to indicate the type of force
What is the general structure of a free body diagram ?
A box with arrows going outwards
In which direction does the applied force go on a free body diagram?
To the right
Which forces do we draw on a free body diagram?
The most affecting forces
How can we see if an object is moving at constant velocity on a free body diagram and why?
The arrows are the same size, meaning there’s no net force
How can we tell when there’s no net force on a free body diagram? What does this mean?
When the sizes of the arrows are the same - it’s moving at constant velocity
Describe the forces when an object is moving at constant velocity
No net force
What do forces tell us ?
What our accelerations are
What do forces NOT tell us?
What our velocities are
Do forces tell us our accelerations or velocities?
Accelerations
Does a larger force in a particular direction mean that an object is travelling in that direction? Why?
No
Forces tell us what our acceleration is, not velocity
Newton’s 1st law
Every object remains in a state of motion in a straight line at constant speed unless an external force acts upon it, forcing it to change
What’s “every object remains in a state of motion in a straight line at constant speed unless an external force acts upon it, forcing it to change”?
Newton’s 1st law
What does an object do if its resultant force i 0N?
Remains stationary or continues moving at a constant velocity
What’s the resultant force on an object if its remaining stationary or is moving at a constant velocity?
0N
What do unbalanced forces do?
Cause a change in the motion of a body
What causes a change in the motion of a body?
Unbalanced forces
Describe the motion an object remains in unless acted on by an external force under Newton’s 1st law
In a straight line, at constant speed
Newton’s 2nd law
The rate of change of momentum of an object is in proportion to the amount of force acting upon it and the direction of this force
Force = mass x acceleration (ΣF=ma)
Whats ‘The rate of change of momentum of an object is in proportion to the amount of force acting upon it and the direction of this force’?
Newton’s 2nd law
What is the rate of change of momentum of an object in proportion to? According to what?
The amount of force acting upon it and the direction of the force
Newton’s 2nd law
What’s the rate of change of momentum’s relationship to the amount of force acting upon it and the direction of this force? According to what?
In proportion
Newton’s 2nd law
Equation for Newton’s 2nd law
Force = mass x acceleration
ΣF = ma
What is ΣF=ma the equation for and what does it stand for?
Newton’s 2nd law
Force = mass x acceleration
Newton’s 3rd law
If object A exerts a force on object B, then B exerts an equal (in size) but opposite (in direction) force on object A
What’s ‘If object A exerts a force on object B, then B exerts an equal (in size) but opposite (in direction) force on object A’?
Newton’s 3rd law
What do we always label first on a free body diagram?
Weight
Which force isn’t present on ice?
Friction
On what type of surface is friction not present?
Ice
Is there applied force when an object is sliding in a specific direction? Why?
No - there’s nothing actually touching the object
Which force isn’t present when an object is sliding in a certain direction? Why?
Applied as there’s nothing actually touching the object
If something is in the air and we’re told to ignore air resistance, what are the forces acting on an object?
Only weight
When is the only force acting on an object its weight?
When it’s in the air and we’re told to ignore air resistance
How do we label air resistance?
Remember it’s always in the opposite direction of motion
Name a particular type of applied force
Buoyancy
Buoyancy
A particular type of applied force, when something floats
What type of force is buoyancy?
Applied
In which direction does the normal force always act?
Not straight up - 90 degrees to the surface
Which force doesn’t always act straight up - which direction is it therefore?
Normal force - always 90 degrees to the surface
Fres meaning
Frictional force
What’s the difference between using Fair resistance and Fdrag?
Fair resistance - 2 solids
Fdrag - fluids, air…
Which notation for the air resistance force is used for 2 solids?
Fresistance
Which notation for the air resistance force is for fluids, air…
Fdrag
Fair resistance notation - what’s it for?
2 solids
Fdrag air resistance notation - what’s it used for?
Fluids, air…
In which direction is the spring force?
Always in the direction of the spring
Which force is always in the direction of a spring?
Spring force
Symbol for momentum
p
p symbol meaning
Momentum
What is momentum?
The product of an objects mass and velocity
The product of an objects mass and velocity
Momentum
Momentum unit
Kgms^-1
What type of quantity is momentum and why?
Vector quantity, as velocity is too
What happens to the value of momentum if it’s in the opposite direction of another object?
Becomes negative
When does momentum become negative?
When in the opposite direction
Equation for linear momentum
p =mv
(Momentum = mass x velocity)
p = mv equation
Momentum
(Mass x velocity)
How can Newton’s second law be written in order for us to receive “impulse”?
F = ma
a = Δv
——
Δt
F = m x Δv
——
Δt
F x Δt = m x Δv
(F x Δt = impulse)
Impulse formula
F x Δt
Define the sections of the other way to write Newton’s second law
m x Δv
A change in momentum which happens when something’s velocity changes
F x Δt
The force that causes this change in momentum multiplied by the time taken for the change
What does impulse represent?
Change in momentum
Impulse formula
F x Δt
F x Δt
Impulse
What type of quantity is impulse and why?
Vector quantity as velocity is also one
What’s the difference in being able to use the new way of writing Newton’s second law?
Can now apply to situations where a change in mass as well as a change in velocity occurs
Equation to use for Newton’s second law when the mass a well as velocity changes
F x Δt = m x Δv
Impulse unit
N
Definition of a Newton
The force which causes a rate of change of momentum of one kilogram metre per second per second (N)
The force which causes a rate of change of momentum of one kilogram metre per second per second
Newton
N actual units
Kgms-2
What does Newton’s second law state?
When a resultant external force acts on a body, it is accelerated in the direction of the force; the magnitude of the acceleration is directly proportional to the force and inversely proportional to the mass of the body
(F = ma)
What is directly proportional under Newton’s second law?
Magnitude of the acceleration and the force
What is inversely proportional under Newton’s second law?
Mass and acceleration
When is a body accelerated in the direction of a force?
When a resultant force acts on a body
Why does the Kgms-2 unit stand for N?
F = ma
Kgms-2 = kg x ms-2
(Force is defined by these laws)
What’s the alternative way of looking at Newton’s second law?
F = mv - mu
————. (=ma)
Time taken
F = mv - mu
————. (=ma)
Time taken
Which other equation make this one make sense?
a = (v-u)
——
t
What type of quantity is momentum?
A conserved quantity
Express, in a sentence, how momentum is conserved during an incident
“The sum of the momenta before an incident is equal to the sum of the momenta after the incident, provided that no external forces act”
Under which conditions is the sum of the momenta before an incident equal to the sum of the momenta after the incident?
No external forces acting
What is the “incident” in which momentum is conserved?
A collision
Equation to express the conservation of momentum during a collision
Momentum before collision = momentum after collision
m1u1 + m2u2 = m1v1 + m2v2
What does m1u1 + m2u2 = m1v1 + m2v2 represent?
The conservation of momentum
(Momentum before collision = momentum after collision)
Elastic collisions
When two objects collide and then travel independently of each other and there’s no loss of kinetic energy
When two objects collide and then travel independently of each other
Elastic collisions
What happens to kinetic energy during elastic collisions?
No loss of kinetic energy
Express the kinetic energy in an elastic collision in a worded equation
The sum of the KE before the collision = the sum of the KE after the collision
Which type of collision causes no loss of kinetic energy?
Elastic collisions
Which equation do we use for elastic collisions?
m1u1 + m2u2 = m1v1 + m2v2
How can we check if a collision is elastic?
Calculate the sum of kinetic energy before and after the collision to check if its elastic
What type of quantity is kinetic energy?
Scalar
Kinetic energy equation
E = 1/2mv^2
Inelastic collisions
When particles collide and become stuck together and there’s loss on kinetic energy
When particles collide and become stuck together
Inelastic collisions
Which type of collision causes a loss of kinetic energy?
Inelastic collisions
What happens to the equation we use with Inelastic collisions and why?
Is modified since the final velocity is the same on both sides
Equation for Inelastic collisions
m1u1 + m2u2 = (m1 + m2)v
How do we prove that a collision is Inelastic?
Show that the sum of the KE after the collision is less than the sum for the KE before the collision
Which force does Newton’s second law calculate?
The resultant
Are momentum and newton’s units the same?
No
Momentum - kgms^-1
Newton - kgms^-2
If something is collided into, what is its initial velocity?
0ms^-1
What is the principle of conservation of momentum?
The sum of the momenta before an incident is equal to the sum of the momenta after the incident - provided that no external forces act
What do we need to remember if doing momentum questions and thing that’s being collided into is moving towards the thing colliding into it?
Velocity is a vector, so it has direction and will need to be negative if moving left
Describe Newton’s second law in terms of momentum
A body’s rate of change of momentum is proportional to the resultant force acting upon it
F = change in momentum
——————————
change in time
When must you multiply uncertainty by 2?
If it’s squared in the formula
What must you do to uncertainty if it’s squared in a formula?
x2
When do we add % uncertainties and when do we add absolute uncertainties?
Adding or subtracting - add ABSOLUTE uncertainties
Multiplying or dividing - add PERCENTAGE uncertainties
What will happen to a boat when a ball is caught on the opposite side to the side it was thrown from and why?
The boat will decelerate and eventually come to rest again - force in the opposite direction, conservation of momentum
Describe the force if something accelerates uniformly
Constant force forward
Describe the force is something decelerated uniformly
Constant force backwards
