Mechanics Flashcards
Four equations of motion
v=u+at
s=ut+1/2at^2
v^2=u^2+2as
S=1/2(u+v)t
what does the gradient on a velocity time graph mean
straight = Constant
acceleration
Curved = Changing acceleration
Newtons First law
an object will remain at rest or move with a constant velocity unless acted on by a resultant force. If the net force is zero, then the object will not change its state of motion. This is also known as the law of inertia, because it implies that objects resist changes in their motion.
Newtons second law
Force (N) = mass(kg) x acceleration (ms^-2)
- use when an object experiences a resultant force (accelerating or deaccelerating)
Newtons third law
For every action there is an equal and opposite reaction
- “if object A exerts a force on object B then object B exerts an equal and opposite force on object A”
Third law rules
- equal in magnitude
- opposite in direction
- the same type of force
- acting on different objects
mass of earth
6 x 10^24
size of an atom
10^-10 - 10^-15
why does the earth move towords a person using newtons third law
When a person stands on the Earth, the Earth exerts a gravitational force on the person, pulling them down. This is the person’s weight. According to Newton’s third law, the person also exerts a gravitational force on the Earth, pulling it up. This force is equal in magnitude but opposite in direction to the Earth’s force on the person2
However, the person does not notice this force because it is very small compared to the Earth’s mass. The Earth’s mass is about 6 x 10^24 kg, while the average human mass is about 70 kg. This means that the Earth’s acceleration due to the person’s force is about 10^-23 m/s^2, which is negligible. The person’s acceleration due to the Earth’s force is about 9.8 m/s^2, which is noticeable3
Therefore, the Earth does move towards the person, but by a very tiny amount that is impossible to measure.
what is statics?
statics is the section of mechanics that studies objects that are in static equilibrium. in other words - objects that are moving at a constant velocity or are stationary. the key concept to apply is: the sum of the forces = 0
EF = 0
force is a vector
what are dynamics?
Dynamics is the section of mechanics that studies the motion of bodies under the action of forces
in other words- objects that are accelerating due to a net resultant force.
The key concept to apply is: The sum of the forces = m x a
or EF=ma
Force is a vector
how to resolve a vector
1.Draw a sketch of the vector and its components, using a right-angled triangle.
2. Label the magnitude and direction of the vector, and the angle it makes with the horizontal or vertical axis.
3.Choose a suitable coordinate system, such as x and y, for the components.
4.Use trigonometry, such as sine and cosine, to find the magnitude of the horizontal and vertical components.
5. Remember that the horizontal component is adjacent to the angle, and the vertical component is opposite to the angle.
pythagoras formula
a^2+b^2=c^2
only usable on right angle traingles
Soh
sin(x)=Opposite/Hypotenuse
cah
cos(x)= adjacent/hypotenuse
toa
tan(x)=opposite/adjacent
Cosline rule
Cos(A)=b^2+c^2-a^2/2bc
a^2=b^2+c^2-2bcCos(A)
sin rule
when working out side=
a/Sin(A)=b/Sin(B)=c/Sin(C)
when working out angle=
Sin(A)/a=Sin(B)/b=Sin(C)/c
Displacement- time graph?
This graph shows how the displacement (position) of an object changes over time
gradient of displacement - time graph?
The gradient of the graph is the velocity of the object. The steeper the graph, the faster the object is moving. A horizontal line means the object is at rest. A curved line means the object is accelerating or decelerating.
