3.8.1.3. Exercise: Creating and accessing dictionaries 3#
Someone pushes a carriage using a dynamometer as picture in Fig. 3.8. The push force and position are measured in newtons and metres every tenth of a second, during five seconds.
push_force = [
91.19, 99.22, 93.11, 91.76, 94.93, 96.54, 92.27, 96.01, 92.48,
94.89, 91.55, 90.82, 97.91, 93.19, 95.65, 93.07, 93.65, 90.57,
98.71, 99.97, 95.72, 96.27, 92.67, 93.4 , 98.84, 92.63, 97.03,
93.93, 98.34, 95.82, 99.39, 99.29, 92.74, 90.29, 94.57, 90.69,
93.16, 95.01, 93.16, 97.04, 97.23, 98.9 , 90.26, 97.46, 92.4 ,
90.84, 97.39, 93.56, 97.47, 93.93
]
carriage_position = [
111.5, 111.613, 111.73, 111.852, 111.98, 112.103, 112.225, 112.34,
112.452, 112.567, 112.692, 112.818, 112.952, 113.085, 113.228, 113.37,
113.52, 113.666, 113.813, 113.969, 114.13, 114.296, 114.454, 114.602,
114.749, 114.887, 115.033, 115.186, 115.347, 115.511, 115.676, 115.844,
116.017, 116.199, 116.386, 116.568, 116.745, 116.922, 117.095, 117.262,
117.424, 117.592, 117.757, 117.931, 118.113, 118.289, 118.469, 118.644,
118.826, 119.001
]
Write a function named calculate_speed_and_power that would have this docstring:
def calculate_speed_and_power(force, position, sampling_frequency):
"""
Calculate speed and power based on force and position.
Parameters
----------
force : list[float]
A list of forces in newtons.
position : list[float]
A list of positions in meters. Its length must be the same as `force`.
sampling_frequency : float
The frequency at which the positions were measured in Hz.
Returns
-------
list[dict]
A list of the same length of `force` and `position`, that contains
dictionaries with the following keys:
- "Force": force in newtons
- "Position": position in meters
- "Speed": speed in m/s
- "Power": power in watts.
Example
-------
To get the power at the 5th sample, we would do:
>>> data = calculate_speed_and_power(force, position, sampling_frequency)
>>> power_5th_sample = data[4]["Power"]
"""
Tip
You are strongly encouraged to reuse the functions calculate_speed and calculate_power that you wrote in Exercise: Looping using for and range 3 and Exercise: Looping using for and range 4.
Show code cell content
def calculate_speed(position, sampling_frequency):
"""
Calculate speed based on position.
Parameters
----------
position : list[float]
A list of positions in meters.
sampling_frequency : float
The frequency at which the positions were measured in Hz.
Returns
-------
list[float]
A list of speeds in m/s. This list is the same size as `position`.
Since speed cannot be calculated on first and last time, values
of zero are returned for these times.
"""
speed = [0] # First element
# Calculate speed for every element but first and last
for i in range(1, len(position) - 1):
speed.append((position[i+1] - position[i-1]) * sampling_frequency / 2)
speed.append(0) # Last element
return speed
def calculate_power(force, speed):
"""
Calculate the power according to force and speed.
Parameters
----------
force : list[float]
A list of forces in newtons.
speed : list[float]
A list of speeds in m/s. Its length must be the same as force.
Returns
-------
list[float]
A list of powers in watts.
"""
power = [] # Initialize the output list
for i in range(len(force)):
power.append(force[i] * speed[i])
return power
def calculate_speed_and_power(force, position, sampling_frequency):
"""
Calculate speed and power based on force and position.
Parameters
----------
force : list[float]
A list of forces in newtons.
position : list[float]
A list of positions in meters. Its length must be the same as `force`.
sampling_frequency : float
The frequency at which the positions were measured in Hz.
Returns
-------
list[dict]
A list of the same length of `force` and `position`, that contains
dictionaries with the following keys:
- "Force": force in newtons
- "Position": position in meters
- "Speed": speed in m/s
- "Power": power in watts.
Example
-------
To get the power at the 5th sample, we would do:
>>> data = calculate_speed_and_power(force, position, sampling_frequency)
>>> power_5th_sample = data[4]["Power"]
"""
# Calculate speed based on position
speed = calculate_speed(position, sampling_frequency)
# Calculate power based on speed and force
power = calculate_power(force, speed)
# Generate a list of dictionaries with this information
output = []
for i in range(len(position)):
output.append(
{
"Force": force[i],
"Position": position[i],
"Speed": speed[i],
"Power": power[i],
}
)
return output
# Test it
data = calculate_speed_and_power(
push_force,
carriage_position,
sampling_frequency=10
)
data[4]
{'Force': 94.93,
'Position': 111.98,
'Speed': 1.2549999999999528,
'Power': 119.13714999999553}