2 Mechanics Flashcards
When can suvat equations be used?
When an object is moving at a constant velocity or accelerating at a constant rate
What are the suvat equations?
S=(u+v)t/2
V=u+at
S=ut+1/2at^2
V^2=u^2+2as
What is the gradient on a displacement against time graph?
Velocity
What is the area under the graph on a velocity against time graph?
Distance
What is the gradient on a velocity against time graph?
Acceleration
What is the area under the graph of an acceleration against time graph?
Velocity
What is a vector?
Quantities with a magnitude and direction
What is a scalar?
Quantities with s magnitude but no direction
How can the magnitude of a 2 perpendicular vectors be worked out?
Pythagoras
How can you split vectors into horizontal and vertical components?
Using SOHCAHTOA
What are distant forces?
Forces acting over a distance e.g gravity
What are contact forces?
Forces acting at a point e.g friction
What is Newton’s first law?
A body will remain at rest or move at a constant velocity unless acted upon by an external resultant force
What is Newton’s second law?
F=ma for a body of fixed mass, the acceleration is directly proportional to the resultant force applied to the body
Newton’s third law
If body A exerts a force in body B, then body B will exert an equal and opposite force on body A
For forced to be considered as force pairs they must:
- act on two separate bodies
- be if the same type
- act along the same line
- be equal in magnitude
- act in opposite directions
What equipment helps when trying to calculate gravity?
- small heavy ball to minimise air resistance
- having computer automatically release and tine the ball means you can measure with a smaller uncertainty
- making h larger to reduce percentage uncertainty
What equipment is good for measuring projectile motion?
Video camera or strobe photography
What things affect friction?
- speed of object
- shape of object
- viscosity of fluid
What 3 things need to be remembered about frictional forces?
1) they always act in the opposite direction to motion
2) they can never speed things up
3) they convert KE into heat and sound
What two things are needed to reach terminal velocity?
- a driving force that stays the same all the time
* a frictional or drag force that increase with velocity
Equation for momentum
P=mv
Momentum= mass x velocity
Equation for work done
W=fxd
Work done= force x displacement in direction of force
Equation for power
P=E/t
Power= energy transferred/ time
What is one watt equal to?
1 joule per second
Equation for KE
KE=1/2mv^2
Equation for GPE
GPE=mgh
Equation for efficiency
Eff=useful energy output/ total energy input
What is the relationship between mass and change in velocity?
The greater an objects mass, the greater it’s resistance to a change in velocity
What is the centre of gravity
The single point of an object that you can consider the the whole weight to act through
What experiment can be used to find the centre of gravity of an irregular object?
1) hang the object freely from a string
2) draw a vertical line downwards from the string using a plumb line
3) have the object from a different point
4) the centre of gravity is where they cross
When will an object topple over?
When the vertical line drawn downwards from its centre of gravity falls outside its base area because the objects weight is causing a turning force
Equation for moments
Moment=force x perpendicular distance to pivot
Principle of moments
For a body to be in equilibrium the sum of the clockwise moments about any point equals the sum of the anti-clockwise moments
What is impulse?
Change in momentum (mv/t)
Conservation of linear momentum
The total momentum of any interacting bodies is conserved, provided that no resultant external force acts in the system
Efficiency equation
(Useful energy or power out)/ (total energy or power in)
