Y3 physics for fe Flashcards
Explain vt grpah of falling stone (neglect air resistance)
Gravitational acceleration near the earth’s surface has a constant direction and magnitude regardless of motion of body
Systematic errors
All readings or measurements are always above or below true value by a fixed amount (eg not accounting for zero error)
Systematic errors
All readings or measurements are always above or below true value by a fixed amount (eg not accounting for zero error)
Whats random errors
Readings and measurements being scattered about a mean value. Equal chances being +ve or -ve
(reduced by repeating measurement and averaging, plotting graph and drawing line of best fit)
Newton First Law
An object at rest remain at rest and an object in motion will continue in motion at constant velocity in the absence of resultant force acting on it
Newton 2nd law
The rate of change of momentum of a body is directly proportional to the resultant force acting on it and direction of resultant force is in direction of change in momentum
Newton Third law
If A exerts a force on B, B exerts equal and opposite force on A
Desrcibe the motion of a particle falling (include air resistance)
As the particle is falling, the gravitational force acting on it will result in an initial downward acceleration of 9.81ms-2, hence speed increase from A to B.
With an increasing speed, air resistance acting on stone increase. This cause net acceleration of stone to decrease Thus stone acceleration decrease from B to C
Criteria of action reaction pair
Same type
Equal in magnitude
Act in opposite direction
Act on diff bodies
define moment about a point
force x perpendicular distance from point to the line of action of force
Principle of moments
For a body in equilibrium, the algebraic sum of the moments of all the external forces on the body about any axis is zero
Sum of clockwise moments = sum of anticlockwise moments
how determine CG for an irregular object
1) Suspend lamina at one end using a pin on retort stand and hang the plumbline from the pin. Use ruler and draw vertical line shown by the plumbline.
2) Hang Lamina from other end and place plumbline in front of lamina. Use ruler and draw new vert. line shown
3) Intersection between the two lines is the CG of object. Can check by repeating step 2 using a third point of suspension
· Precautions: hole small so not too much of lamina removed
· Lamina should be free to swing abt its point of intersection
how ncrease stability
Centre of Gravity (CG) as low as possible (more mass packed at the bottom)
· Base area as wide as possible
.How know whether object will topple
When line of action of CG lies within its base, there is a clockwise/anticlockwise moment about point due to the weight. The object wont topple.
When line of action of CG lies outside its base, there is an clockwise/anticlockwise moment about point due to the weight. Object will topple.
Object is in equilibrium if its in:
a) Translational equilibrium i.e. the resultant force acting on it is 0
b) Rotational equilibrium I.e., the resultant moment acting on it is 0
