P2 Flashcards
How many seconds in a hour, how many meters in a mile
3,600s = 1h
1609m = 1 mile
How can a force change an object
It can change the shape or the motion. It can accelerate a body.
Forces are represented with Newtons(Vector’
What is newton’s third Law?
When two bodies interact they exert a force on each other , equality in size but opposite in direction
Give an example of a non contact force
Gravitation field, magnetic, electrostatic
A free body diagram shows
The result force
How do you calculate free bodies in the horizontal and vertical plane?
Pythagoras Theorem , but make sure the diagram is tip to head
To find the direction of the pythagora’s Theron :
Find the degree of the angle using trig.
The angle comes off at the new line and thE largest quantity
How would you resolve a force?
You have to find the horizontal and vertical plane of a diagonal line . You would use trigonometry using the angle and the resultant force. Then do two separate equations to find the two separate values.
Or scale diagram
What is Newton’s first law?
A body will remain at rest on continue at uniform velocity unless acted upon by a resultant force
What is inertia ?
How difficult it is to change the velocity of a body.
The greater mass, the greater interia
What is Newton’s second law?
The acceleration experienced by a body is directly proportional to the resultant force
What is the equation of newton’s 2nd Law
F= M A
N= kg m/s**2
What is magnitude?
The size of something
What is the difference between a scalar and a vector quantity ?
A vector has magnitude and direction whereas a scalar quantity only has magnitude
What is acceleration?
The rate of change of velocity.
If direction or speed changes so does acceleration
V - U
———
T
Why is a body moving in a circle at constant speed have a resultant force?
It’s changing direction and therefore velocity, constantly accelerating which means (N’s 1st law) there is a resultant force.
This resultant force is known as centripetal force
What is terminal velocity?
Constant velocity , zero resultant force
Describe a parachuter’s journey
- Weight acts down, no a lot of drag, RF increases down, acceleration, increasing velocity
- Air resistance increases to the point where RF is zero, terminal velocity - no acceleration & constant velocity
- Remains until parachute is opened, SA increases, increasing drag. RF is acting upwards, decreasing velocity
- As velocity decrease so does drag so eventually the RF becomes zero again, terminal velocity 2, contact velocity, zero acceleration
Define momentum
How difficult it is to stop a moving body. The two factors affecting this are mass and velocities.
(A vector value)
How do you calculate momentum? 🅿️
Mass * velocity = momentum
Kg * m/s = kg m/s
What is the law of conservation of momentum?
The total momentum before an event is equal to the total momentum after an event .
How do you apply the LofM when two stationary bodies push and move away from each other?
Eg (explosion)
The total momentum before and after must equal zero , as they were stationary.
To calculate a total:
. Calculate the first object using P = mv
. Then calculate the second object by knowing the fact the Momentum is negative, to equal zero, as they were going in opposite directions
How do you use the L of C when two bodies collide and move off together?
Calculate the total before , by calculating each separate component’s momentum and adding them together.
Calculate the total after but appreciate it as one value , use the momentum of previous to find out other variables
What is work?
The transfer of energy .
Whenever a force acts upon an object, work is done
What is the work equation?
Work done = force * distance
J = N *m
What happens in term of energy when work is done?
Energy is transferred from one form to another.
Eg : kinetic to gravitational potential energy,
When a body is lifted
What is power?
The rate of energy transfer
What is the power equation?
P = E/T
W= J / s
How do you calculate the gravitational force?
Gravitational force = mass * gravitational field strength
N = kg * (N/ kg)
The gravitational field strength is always 10 N/kg on earth
What is the kinetic energy formula?
Kinetic energy = 0.5 ✖️mass ✖️ (speed2)
J =. Kg* (m/s)2
E= 1/2 mc squared
What is the potential energy formula?
Potential energy = mass * height * gravitational field strength
J = kg * m * (N / kg)
U=mgh
What is an elastic body?
Objects that return to their original shape when the deforming force is removed
What is the deforming force?
Stretching , compressing or bending a body to change the shape
What is a plastic body?
Objects that do not return to their original shape when the deforming force is removed
What body is a spring?
Elastic, as they are designed to return to their original position. However if too large of a force is applied they will break.
What is Hookes Law?
The extension of a body is directly proportional to the force applied as long as the limit of proportionality is not exceeded
What is the equation for Hooke’s Law
Force exerted by spring = K✖️extension
N = (N/m) ✖️m
How do you find the extension?
New length - original length
What is the spring constant a measure of?
How stiff the material is.
The larger the konstant ,the stiffer it is
😖
What assumption is made when calculating Hooke’s Law
The limit of proportionality has not yet been reached
On a force Extension graph what is the gradient?
The spring constant
What does a diagonal line show on a Force Extension Graph?
That it obeys Hooke’s law
What does point X show on the graph?
The limit of proportionality, the point just before the line starts to curve
What is the gradient of a distance time graph ?
Speed
What does a steeping curve mean on a DT graph?
Velocity is increasing = acceleration
What does a levelling off curve mean on a DT graph?
Decreasing velocity = deceleration
How do you find the gradient of a curved line?
Create a tangent
What is the area under a V T graph ?
Displacement
What does a steeping curve mean on a VT graph?
Increasing acceleration
What is electrostatic interaction
Occurs between charged particles where they experience a force of attraction or repulsion
What is a contact force?
They are experienced in the opposite direction to contact such as friction
Where does the reaction force act
From point of contact in the opposite direction
Where does weight act?
Always vertically downwards from the centre of the object
What does it mean for a material to be brittle?
It has all linear sections, will snap instead of stretching after the elastic limit.
How do you calculate work done on a force- extension graph
The area under the line
Who would reach the floor first If two people with a different mass jump of a building at the same time?
They would both reach at the same time.
Because F=MA
A=F➗M
F= mass✖️gravitational field (10N/m)
A=(mass✖️gravitational field (10N/m))➗mass
A= gravitational field
A= 10 same for both
What is a moment?
The moment of a force is the measure of its turning effect, about a pivot.
the greater the moment , the easier it is to rotate a body
What is formula for moment’s?
M= d ✖️force
d is the perpendicular distance from the pivot to the the line of action of force (m)
How can the moment of the force be increased?
🟢Increasing the size of the force
🟢increasing the perpendicular distance from thepivot
Are moments scale or vector quantities?
✔️ vector, mention whether they are clockwise or anti-clockwise
What is the principle of moments?
The sum of the clockwise moments about any point = the sum of anti clockwise moments about any points
*nothing is turning
What is a lever?
A force multiplier
A small force on one side of the lever , leads to a large force exerted on the body on the opposite side of the pivot
F1d1=F2d2
What is mechanical advantage?
The number of times a machine multiplies the effort force
*how easier it makes it for you ( to apply less force)
Load(F1)➗effort(F2)
What is a gear?
🟢moment multipliers
🟢 force applied between the gears is the same, the radius of the cogs the moment changes
What it the mechanical advantage of gears?
Output cog radius➗input cog radius
Largest value always as the numerator
What happens to a car when travelling up hill? (Gears)
🟢you change to a lower gear
🟢the means input gear is a small gear is connected to a larger gear
🟢a input larger moment
🟢an output smaller moment
🟢causing the wheel to turn more slowly
*Large mechanical advantage
What happens when a car is travelling down hill?
🟢you change to a high gear
🟢the means input gear is a large gear is connected to a smaller gear
🟢a input smaller moment
🟢an output larger moment
🟢causing the wheel to turn more fast
*Large mechanical advantage
How is pressure exerted in a fluid?
🔴The pressure acts in all directions, and is transmitted without loss
🔴producing a force perpendicular to any surface
How do hydraulic machines work?
(Brakes)
Diagram
🔵use the pressure exerted in liquids to multiply forces and apply them at distance
Describe the structure of hydraulic machines?
🟡two pistons are connected by a pipe full of fluid (oil)
🟡the small force applied to piston 1 acts over a small area 1 creating a pressure within the fluid
🟡 the same pressure acts at piston 2 over area 2
If area 2>area 1 means output force is increased
Which distance would be applicable ?
How are forces transmitted in a liquid ?
In all directions ,
Without any loss
what is the difference between the limit of proptionality and the elastic limit?
the limit of proportionality is the last instance where the force applied and spring constant are directly proportional (Hookes’s law) .
The elastic limit of a material is the furthest point it can be stretched or deformed while being able to return to its previous shape
What is the velocity time graph for a bouncing ball?
What is the velocity time graph for a bouncing ball?
What does it mean for an object to be levitating?
The resultant force must be zero and so the upwards force/ drags must be equal to the weight force (mg).
What does it mean to be directly proportional?
A straight line passing through the origin
What is a ‘zero error’.
When a reading is displayed of an instrument, when the true reading is zero
Part a
Part b
Part c
how many forces must be applied to stretch, bend or compress an object?
moe than one force, becuase otherwise the object would start moving and wouldn’t hold still
what is the accelertation in free fall
a = 10 m/s2
in the absence of air resistance
how would you define inertial mass?
the ratio of force over acceleration
what is the equation for the work done in sketching?
=0.5 * spring constant * extention
define weight
the force of earth on on object
how would you measure the weight ?
- newton meter
- scales
what is the acceleration of free fall (gravity)?
10m/s
