P10: Forces And Motion Flashcards
What is hooke’s law?
Any spring, whatever the length if you put a force the extention increases in propotion to the mass.
Newtons second law
As the force on an object increases the acceleration increases
DEF:
The acceleration of an object is preporional to the resultant force on an object
Accelration formula
A=v-u/t
Resultant force (N)
Resultant force=mass x acceleration
Resultant force(N) equation
Mass(kg)x acceleration m/s squared
Momentum(p)
Mass(kg)xvelocity m/s squared
Hooke’s law equation
Spring constant(k)=extention of spring(x)
Weight(n)
Mass(kg) x gravity
Change in momentum(p)
P=mv-mu
P=m(v-u)
The greater the resultant force on an object, the greater the object’s ________
Acceleration
What is the equation for the resultant force acting on an object?
F= a x m
What is Newton’s second law of motion?
The acceleration of an object is proportional to the resultant force of an object
The acceleration of an object is inversely proportional to the mass of an object
The resultant force is proportional to the _______________
Object’s mass x its acceleration
You can write this as f= mxa
The greater the resultant force on an object, the greater the object’s _________
Acceleration
The greater the mass of an object, the smaller its acceleration for a ___________
Given force
What is the intertia of an object?
Its tendency to stay at a rest or to continue in uniform motion
If the velocity of an onjects changes, it must be axted on by a___________
Resultant force
The velocity of the object increases if the resultant force is in the _______________
SAME direction as the velocity
The velocity of the object decreases if the resultant force is in the _______________
OPPOSITE direction to its velocity
The inertial mass of an object is __________
A measure of the difficulty of changing the object’s velocity
How can you define the inertial mass?
Force/ acceleration
Why does an object fall if you let go of it above the ground?
Because of its weight
How much does an object acted on by gravity accelerate downwards at a constant acceleration?
9.8 (round it to 10) m/s squared
If I release a 1 kg object above ground ehat is
The gravitational force on it?
What is its acceleration?
Gravitatiojal force= 9,8 N
Acceleration = force/ mass. 9.8 N/ 1 kg = 9.8 m/s squared
What is your weight caused by?
The graviatational force of attraction between you and Earth
-this force is slightly weaker at the equator than the poles.- so you will weigh slightly less at the equator than the poles.
Does your mass change where ever you are?
No
What is weight measured in?
Newtons.
What is mass measured in?
Kg
What is the weight of an object?
The force acting on it due to gravity.
What is the mass of an object?
Depends on the quantity of matter in it
How can you measure the weight on an object?
Using a newton-meter
What is gravitational field strength measured in?
N/kg
What is Earth’s gravitational field strength at its surface?
About 9.8 N/kg
What is the gravitational force on a 1kg object?
The gravitational field strength at the place where the object is.
What is the Equation for the weight of an object?
Weight(N) = mass(kg) x gravitational field strength(N/kg)
If an object falls in fluid what happens?
The fluid drags on the object because of friction between the fluid and the surface of the moving object
-the friction force increases with speed
If an object falls in fluid what happens to the resultant force on the object?
The resultant force on the object is its weight minus the frictional force on it
The acceleration of an object_______ as it falls
Decreases
Why does the acceleration of an object decrease as it falls?
Because the frictional force increases as it speeds up. Therefore the resultant force on it decreases-causing the acceleration to decrease
When does the object reach a constant velocity?
When the frictional force on it is equal and opposite to its weight-this velocity is called terminal velocity
-the resultant force is 0 so the acceleration is 0
What is the acceleration and resultant force at terminal velocity?
0
What is the frictional force when an object moves through the air?
Air resistance
The air resistance on the object is much smaller than the frictional force on an object falling through the liquid in figure 1. What does this mean?
The object would need to fall much further in the air than the water before the object reaches a constant velocity.
What is terminal velocity of an object?
The velocity it eventually reaches when it is falling.
-the weight of the object is equal to the friction force on the object
What is the resultant force when an object is moving at terminal velocity?
0
For any car travelling at constant velocity, what is the resultant force? And why?
0
Because the driving force of its engine is balanced by the resistive forced(which are mostly caused by air resistance)
A car driver uses the accelerator pedal to vary what?
The driving force of the engine
What does the braking force needed to stop a vehicle in a given distance depend on?
- the speed of the vehicle when the brakes are first applied
- the mass of the vehicle
Equation for resultant force:
Mass x acceleration
The greater the speed, the greater the ____________ needed to stop the vehicle within a given distance
Deceleration
Within the same distance, would the braking force be greater?
To stop a car travelling at a low or high speed?
To stop a car travelling at a high speed
The greater the mass, the _________ the braking force needed for a given deceleration
Greater
What is the stopping distance?
The shortest distance a vehicle can safely stop in
What is the stopping distance made out of?
-thinking distance + breaking distance
What is the thinking distance?
The distance travelled by the vehicle in the time it takes to react
(Because the car moves at a constant speed during the reation time the thinking distance is = speed x the reaction time
Is the thinking distance proportional to speed?
Yes
What is the breaking distance?
The distance travelled by the vehicle during the time the braking force acts
What can affecting stopping distances?
- tiredness, alcohol durgs that affect the brain and reaction time
- distractions like phones can increase reaction time
-the faster a vehicle is travelling thr furher it travels before it stops.
(Because the thinking and stopping distance both increase with speed.)
- bad road conditions e.g icy
- poorly maintained vehicles e.g worn brakes and tyres take longer to stop because the brakes and tyres are less effective.
What does the deceleration of a road vehicke depend on?
The friction between the road and car tyres
-to avoid skidding the deceleration should be no more than 6/s squared
Can check this using equation (v squared - u squared)/ 2s
What is the braking force on a vehicle?
F= ma
What is momentum of a moving object measured in?
Kg m/s
What is velocity?
the speed of something in a given direction.
What is the equation for momentum?
Momuntum of a moving object( kg m/s) = mass (kg) x velocity(m/s)
Is momuntum a scalar or vector quantity
Vector because it has both size and direction
In a collision of two trollet’s of the same mass, Trolly A is ________ by the impact
Halved
Is the momentum after the collision the same as the momuntum before the collision?
Yes
What is the law of conservation of momentum?
In a closed system, the total momentum before an event is equal to the total momentum after the event
Momentum is conserved in a collision or explosion as long ss what?
No external forces act on the objects
When you jump of a skateboard it can shoot away from you once you step of it, what does this mean?
Its momentum is opposite to your own momentum
In the results of a test what did it show with two single trolleys recoil and momuntum
The trolleys recoiled sith equal and oppsite momentum
Becaus they had the same mass
When you hit a sauash ball what happens to the shape of the ball?
It changes briefly
How do we know if an object is elastic?
If it returns to its original shape when forces that are deforming it are removed
What is the increase of length from the origin called?
In a spring
Extention
What ks the equation for:
the extention of the strip lf material or spring at ay stage?
Length at the stage - original lenth
The steel spring goves a straight line through the origin,
this shows thst the weight hung on the steel spring is ________ to the extention of the spring
Directly proprtional
(E.g doubling weight from 2N to 4N diubles the extention of the steel spring
What does Hooke’s law state?
If the extnetion of any stretched object or material is directly proportional to the stretching force, the object obey’s Hooke’s law
Hooke’s law equation:
Flrce applied (N)= spring constant (N/m( x entention (m)
If the force is too big, the string strethces more than predicted, this is because the spring has stretched beyond its_____________
Limit of proportionality
Something with a lot of momentum has________
A lot of intertia?
What is inertia?
Objects will continue with the (newton’s first law) same speed and direction (unless a force acts on it).
What is inverse proportion ?
Doubling one auantity caisss the other to half
