ch 1 - kinematics

Question 1

what is average speed?

Answer 1

the total distance travelled divided by the total time taken

v = d/t

Question 2

what is instantaneous speed?

Answer 2

the speed of an object measured over a very short period of time (car’s speedometer tells the instantaneous speed)

Question 3

what are the usual units for speed?

Answer 3

• m s -1 ( SI UNIT)
• cm s -1
• km s -1
• km h -1
• mph

Question 4

how do you measure speed in the lab?

Answer 4

• TWO LIGHT GATES
  . card on trolley breaks first light beam
  . timer starts
  . card breaks second light beam
  . timer stops
  . s = distance between gates/time
• ONE LIGHT GATE
  . leading edge of card breaks light gate
  . timer starts
  . trailing edge passes light gate
  . timer stops
  . s = length of card/time
• TICKER TIMER
  . timer will mark dots at equal time intervals on tape
  . inspect dot patter on tape
  even space - constant speed
  increasing space - increasing speed
  . take distance measurement after every n dots and find time
  . plot distance-time graph
• MOTION SENSOR
  . sensor tansmits regular ultrasound pulses at trolley
  . detects reflected waves and time taken to got there and back
  . computer finds out distance from this
  . computer creates distance-time graph
  . deduce speed from graph

Question 5

what is displacement?

Answer 5

• the distance of a point in the wave from its undisturbed/equilibrium position
• distance travelled in a particular direction
• vector quantity
• symbol = s, units = m

Question 6

what is a scalar quantity?

Answer 6

a quantity which has only magnitude
- time
- mass
- density
- work
- pressure

Question 7

what is a vector quantity?

Answer 7

a quantity which has both magnitude and direction
- force
- weight
- acceleration
- momentum
- velocity

Question 8

what is velocity?

Answer 8

• rate of change of an object’s displacement
• vector quantity
• symbol = v, units = ms-1

v = change in s/ time

Question 9

displacement - time graphs

Answer 9

• gradient = velocity
• steeper slope = greater velocity
• positive gradient = positive velocity
• negative gradient = negative velocity
• straight line = constant velocity
• curved line = changing velocity

Question 10

what is a resultant?

Answer 10

the single vector formed by adding together two or more vectors

Question 11

for vector subtraction…

Answer 11

add the negative vector
a - (b)