G481 -- Mechanics Barebones Flashcards
What’s the SI unit name and symbol for time?
Second, s
What’s the SI unit name and symbol for length/ displacement?
Metre, m
What’s the SI unit name and symbol for force/ weight?
Newton, N
What’s the SI unit name and symbol for pressure?
Pascal, Pa
What’s the SI unit name and symbol for power?
Watt, W
What’s the SI unit name and symbol for energy, work?
Joule, J
Explain how Galileo disproved the idea that ‘heavier objects fall faster than lighter ones’ by Aristotle?
- Two cannonballs with different masses but the same size
- Dropped from the same height (top of leaning tower of Pisa)
- At the same time
- Hit the ground at the same time
- Both have the same uniform vertical acceleration downwards.
Describe an experiment to estimate the acceleration, g, of free fall, include:
- the measurements taken and the instruments used to take the measurements.
- how the measurements are used to estimate acceleration, g.
- an explanation of why the values of g is only an estimate.
Measurements:
•measure distance ball falls, using a metre ruler or tape measure
•measure time of fall using stopwatch (or electronic timer linked to an electromagnetic and trap door.
How the measurements are used to estimate g
• s=ut+ 0.5at^2
• u=0
• G=2s/ t^2
OR
•plot a graph of s against t^2 for various values of s.
• g= 2*gradient.
g is an estimate because:
• drag on ball is ignored
• reaction time on starting & stopping stopwatch (if stopwatch used)
• parallax problems with landing time (if ball is dropped from a wall)
• residual magnetism delays release of ball (if using electromagnetic)
• trapdoor takes time to open (if experiment uses a trapdoor.
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Why can’t f=ma be used when a particle is traveling at very high speeds?
- The mass of the particle increases
* as the speed approaches the speed of light.
The engines of a spaceship develop constant thrust. Explain why the acceleration of the spaceship increases after lift-off?
Considering f=ma
• The mass of the spaceship decreases as it burns fuel
• The weight of the spaceship decreases as it burns fuel so net force (F) on spaceship increases.
• The weight of the spaceship decreases because g decreases with increasing altitude so net force (F) on spaceship decreases.
State the factors which affects the magnitude of the drag force acting in an object on an object falling through air.
- area of the object
- speed/ velocity of object
- surface/ texture/ aerodynamic shape/ streaming lining of object.
- viscosity of air/fluid /air temperature/ air density/
A skydiver jumps from a stationary hot-air balloon several kilometres above the ground.
Describe and explain the motion of the skydivers in terms of acceleration and forces immediate after jumping.
- speed=0
- drag=0
- net force=weight
- acceleration= g vertical downwards.
A skydiver jumps from a stationary hot-air balloon several kilometres above the ground.
Describe and explain the motion of the skydivers in terms of acceleration and forces at a time before terminal velocity (during free-fall) in reached.
- speed has increased
- drag has increased (drag proportional to speed squared)
- weight is greater than drag
- net force has decreased (net force = weight - drag)
- net force F = ma therefore acceleration is less than g vertical downwards.
A skydiver jumps from a stationary hot-air balloon several kilometres above the ground.
Describe and explain the motion of the skydivers in terms of acceleration and forces a terminal velocity (during free-fall).
- speed has increased to a constant value
- drag has increased (drag is proportional to speed squared)
- weight = drag
- net force = 0
- net force F = ma therefore acceleration is zero
What’s the SI unit name and symbol for mass?
Kilogram, kg
