This first law is rather abstract since we can't quantify this law however it is very common, just like a common sense and we experienced it almost everyday in our life.
The statement:
"A physical object tend to stay at rest or in a motion at a constant speed unless there is an external force acted on the system"
In another words, if there is no external forces,
An object would maintain its speed forever either the speed is zero or a constant speed.
Therefore, First Law and Second Law are strongly related since Second Law is describing the meaning of external force.
On the other hand, law of intertia also suggested that the massive the physic object, more force is needed to move the object from at rest or change its speed.
These example are very common in our daily life. Hence, the first law highlight the importance of MASS in a motion.
Played some calculation game,
How much of EXTERNAL FORCE needed to move a car from rest to 50km/h in 1 minute with the following model:
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Acceleration from 0 to 50km/h in 1 minutes = 0.2315 m/s/s
#1: Perodua Axia [1]
Mass = 820 kg
So, F = ma = 820 x 0.2315 = 189.83 N
Hence, it takes 189.83N of Force to move Axia from rest to 50km/h
#2: Honda Fit/Jazz [2]
Mass = 1070 kg
Hence, it takes 247.71N of Force to move Fit/Jazz from rest to 50km/h
#3: Nissan GT-R [3]
Mass = 1740 kg
Hence, it takes 402.81N of Force to move GT-R from rest to 50km/h
These three examples showed that the greater the mass, the greater the inertia effect such that more force is needed.
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Alright, force is not your language, how about energy or we prefer to call it WORK. Because we know the energy density of gasoline is 34.2 MJ/Litre [4]
It means every 1 litre of gasoline burnt would produce 34.2 MJ of energy through 100% combustion efficiency.
You may ignore the picture, but just to show the relationship among force, energy and work:
 |
| Derivation of Work Done = Change in Kinentic Energy |
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#1: Perodua Axia
Mass = 820 kg
So, Work Done = Change in Kinetic Energy = 79.1 kJ
Hence, 2.31mL of gasoline to be burnt to move Axia from rest to 50km/h
#2: Honda Fit/Jazz
Mass = 1070 kg
So, Work Done = Change in Kinetic Energy = 103.2 kJ
Hence, 3.01mL of gasoline to be burnt to move Jazz/Fit from rest to 50km/h
#3: Nissan GT-R
Mass = 1740 kg
So, Work Done = Change in Kinetic Energy = 167.8 kJ
Hence, 4.90 mL of gasoline to be burnt to move GT-R from rest to 50km/h
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As you can see from these three example under ideal condition, it is clear that the MASS of the vehicle play important role in fuel economy although they are just performing the same operation.
In reality, it might burn 10 times more fuel to overcome the road friction, air drag and compensate the engine and power transmission inefficiency. So you multiply the above value 10 time, you realize that you are burning more gasoline.
On the other hand, Newton's First Law also taught us that how inefficient our cars was during slowing down.
Take example like Honda Fit/Jazz,
Your car is burning 3.01 mL of fuel when you reached 50km/h from 0.
You can't stop burning the fuel, otherwise the speed would drop.
Suddenly, you applied brake where your car stopped from 50km/h to 0,
Imagine it is an IMMEDIATE brake.
Similarly, it applied the same work to stop your car to stop from 50km/h which is 103.2 kJ of work.
Luckily, you have braking system, so you can just apply small amount for work from your feet to apply the same work to stop the car.
Unfortunately, the same amount of fuel the car burnt would be wasted in the form of HEAT instead of mechanical energy to move your cars.
Each time you apply brake, each time you are wasting your fuel.
By understanding First Law and Second Law, don't ever perform immediate brake. It hurt your car and it wasted more fuel than you imagine.
Luckily, scientist invented an interesting device known as Kinetic Energy Recovery System (KERS) [5]. If you drove a manual car, you will apply clutch to disconnect the engine and the wheel. With KERS, some of the mechanical energy in wheel would be stored instead of 100% dissipated into heat loss.
The stored energy can be used to charge the battery so only electrical cars or hybrid electrical cars is more suitable to adopt this technology.
Surprisingly, Formula One was using KERS first.
Lastly, once again, THANKS to the Physic Legend who taught us that MASS is everything before considering the driving pattern.
So what would be my next topic???
In fact, this is a warm up topic for my next topic because consumer should really concern the relationship between the engine size and the mass of the vehicle.
For example,
"Why does the engine size of a car increased as the mass of the car is increased?"
Next topic:
so
STAY TUNED
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