If the resultant force on a stationary object is zero, the object will remainstationary. If the resultant force on a moving object is zero, it'll just carry on moving at the samevelocity
Newton's second law
the acceleration of an object is proportional to the resultantforceacting on the object, and inverselyproportional to the mass of the object
Newtons third law
whenever twoobjectsinteract, the forces they exert on each other are equal and opposite
Vector Quantities
force
velocity
displacement
acceleration
momentum
Scalar Quantities
speed
distance
mass
temperature
time
A force is a push or a pull on an object that is caused by it interacting with something
Contact Forces
friction
airresistance
tension
Non-contact Forces
magnetic force
gravitational force
electrostatic force
Weight is the force acting on an object due to gravity
Measured in newtons
The resultant force is the overall force on a point or object
when a force moves an object through a distance energy is transferred and work is done on the object
Elastic objects can stretch, compress or bend
An object has been elastically deformed if it can go back to it's originalshape and length after the force has been removed
The limit of proportionality is where the extension is no longer proportional to force
A force or several forces can cause an object to rotate
The turning effect of a force is called it's moment
Levers increase the distance from the pivot at which the force is applied. This means lessforce is needed to get the same moment, making it easier to do work
Gears
teeth interlock so that turning one causes another to turn in the opposite direction
used to transmit the rotational effect of a force from one place to another
a force transmitted to a larger gear will cause a biggermoment, as the distance to the pivot is greater
the larger gear will turn slower than the smaller gear
As the depth of the liquid increases, the number of particlesabove that point increases. The weight of these particles adds to the pressure felt at that point, so liquidpressureincreases with depth
When an object is submerged in a fluid, the pressure of the fluid exerts a force on it from everydirection
Pressure increases with depth so the force exerted on the bottom of the object is larger than the force acting on the top of the object. This causes a resultantforceupwards, known as upthrust
The upthrust is equal to the weight of fluid that has been displaced by the object
If the upthrust on an object is equal to the object's weight, then the forces balance and the object floats
If an object's weight is more than the upthrust, the object sinks
An object that's lessdense than the fluid it is placed in weighs less than the equivalent volume of fluid
This means it displaces a volume of fluid that's equal to it's weight before it's completely submerged.
At this point, the object's weight is equal to the upthrust, so the object floats
An object that's denser than the fluid it's placed in is unable to displace enough fluid to equal it's weight.
This means that it's weight is always larger than the upthrust, so it sinks
Atmospheric Pressure is created on a surface by air moleculescolliding with the surface
As the altitude increases, the atmospheric pressure decreases because the atmosphere gets lessdense, so there are fewer air molecules that are able to collide with the surface
Velocity is speed in a given direction
Typical Speeds
person walking - 1.5 m/s
person running - 3 m/s
person cycling - 6 m/s
car - 25 m/s
train - 30 m/s
plane - 250 m/s
sound - 330 m/s
Factors Affecting Something's Speed
fitness
age
terrain
Acceleration is the change in velocity in a certain amount of time
Uniform acceleration is constantacceleration
If an object has no force propelling it along it will always slow down and stop because of friction
friction always acts in the opposite direction to movement
to travel at a steady speed, the driving force needs to balance the frictional forces
Drag is the resistance you get in a fluid
to reduce drag, you can keep the shape of an object streamlined. This is where the object is designed to allow the fluid to flow easily across it, reducing drag
when a falling object first sets off, the force of gravity is much more than the frictional force slowing it down, so it accelerates
as the speed increases, the friction builds up
this gradually reduces the acceleration until eventually the frictional force is equal to the accelerating force
It will have reached terminal velocity and will fall at a steady speed
air resistance causes things to fall at different speeds
terminal velocity of any object is determined by it's drag in comparison to its weight
the frictional force depends on it's shape and area
Inertia is the tendency to continue in the samestate of motion
an object's inertial mass measures how difficult it is to change the velocity of an object
In a closed system, the total momentum before an event is the same as after the event. This is called conservation of momentum
when a non-zero resultant force acts on a moving object it causes it's velocity to change. This means that there's a change in momentum
The force causing the change is equal to the rate of change of momentum