Dynamics Flashcards
What is newtons 1st law?
If the resultant force on an object is zero, then the object will either remain stationary, or if already moving, it will continue to move with uniform motion
What is newtons 2nd law?
The acceleration of a body is directly proportional to the resultant force acting and inversely proportional to the mass of the body
What is newtons 3rd law?
If body A exerts a force on body B, then body B will exert an equal but opposite force on body A
Definition of mass?
A measure of how much matter or material an object has (kg)
Definition of weight?
A measure of how large the force of gravity is on an object (N)
Derive;
A. Resultant F = ma
B. W = mg
F = 🔼 momentum / 🔼 time. = 🔼mv/🔼t
F = m (🔼mv/🔼t). = m (v-u/t)
V-U/ t = acceleration.
So : resultant F = ma
Since weight is a force, we can then calculate
W = mg
Explain newtons 3rd law in terms of forces
Although the two forces are always equal and always opposite, they never cancel each other out as they always act upon different objects
The two things for a newton 3rd pair forces
- one force acts on one body, the other force acts on the other body
- the force exerted by earth on the body is gravitational, so the other force must also be gravitational
Momentum equation and unit
P = mv P = kgms-1
What is the conservation of momentum?
“The total momentum of a system of interacting bodies will remain constant if no external forces are acting”
Momentum is a vector and so has direction
The difference between elastic and inelastic collisions?
Elastic - no energy is lost
Inelastic - energy from collision is lost into surroundings (e.g. Heat, sound)
Give the 10 energy concepts
Sound Internal Chemical Kinetic Heat Electric Nuclear Light Elastic potential Gravitational potential
Definition of work done with equation
If a body moves as a result of a force being applied to it, the force is said to be doing work on the body
Work done = energy transferred
W = F X
Kinetic is energy equation?
1/2 m v^2
🔼 gravitational energy equation
mg. 🔼h
Elastic potential energy equation
1/2 k x^2
What is the work-energy theorem
Substitute ‘a’ from F = ma and into v^2 = u^2 + 2ax
Fx = 1/2 mv^2 - 1/2 mu^2
A force pushing horizontally does work on the object equal to ‘fx’
Conservation of energy?
‘Energy cannot be created or destroyed, only transferred from one form and into another
What is power?
Power is the rate of doing work or the rate of transferring energy
The 2 equations for power
P = W/t
P = E/t
Derive P = Fv
Substituting w for fx = P = Fx/t
However x/t = velocity
Therefore P = Fv
Equation for efficiency
Efficiency (%) = (useful energy / total input energy) X 100
