We are not often aware of ‘impact loading’ in our daily lives, but understanding its principles can make the phenomena that occur around us seem a little more interesting. In this article, we would like to explain this phenomenon using the example of a ‘weighing scale’.
1. what is the difference between a normal load and an impact load?
‘Load’ is the force exerted on an object. Normally, if you gently step on a scale, the scale will point to your weight at rest, i.e. if you weigh 50 kg, you will still weigh 50 kg.
‘Impact load’, on the other hand, refers to the temporary load that occurs when an object is subjected to a force with acceleration. This impact load can be a very large force compared to when the object is at rest.
2. what happens when you jump on the scales?
Let's look at some specific phenomena. When a person weighing 50 kg jumps on the scales, the following things happen
1.Temporary increase in force due to acceleration
When a person ‘jumps’ on the scales, they are accelerating from the air towards the ground. This acceleration causes the scales to be subjected to a force of more than the usual 50 kg at the moment of landing on the ground (i.e. on the scales).
2.The needle jumps up temporarily.
At the moment of landing, the needle on the scales temporarily points to a value of about ‘double’ (around 100 kg). This is because the needle shows a temporarily higher load due to the impact load.
3.Return to a stationary state again.
After landing, when the movement stops, the shock load disappears and the needle returns to the 50 kg position again. This state corresponds to the normal ‘static load’.
3. Calculation of impact loads
The impact load is calculated using the following formula
Meaning of each symbol
F: Impact load in newtons, N
m: Mass of the object (unit: kg)
Δv: Change in velocity of the object (unit: m/s).
Example: change in velocity from just before the fall to a stationary state (0 m/s)
Δt: Time during which the impact occurs (unit: sec, s)
Δt: time during which the impact acts on the object (contact time)
Applying this formula, the calculation in the following problem works out like this.
question: A person weighing 50 kg jumps off a scale from a height of 1 m (surreal conditions...)
Conditions given
Mass: m=50 kg
Height: h=1 m
Contact time: Δt=0.2 s (e.g. time taken to land with the foot)
Gravitational acceleration: g=9.8 m/s2
Calculate the change in velocity (Δv)
Use the free-fall equation to find the velocity immediately before the fall:
Determine the impact load (F)
The point is that the shorter the contact time, the higher the impact load.
(shorter contact times on hard ground and longer contact times on soft mats) In addition, impact loads depend on the speed and mass of the object, so height and speed of movement are important factors.
4. impact loading in familiar examples
The impact load principle is often found in situations other than scales. For example:
How airbags work.
In the event of a car accident, airbags inflate to reduce the impact load, thereby limiting damage to the human body.
Seismic design of high-rise buildings
Seismic isolation and vibration control structures are incorporated to absorb the impact loads caused by shaking during earthquakes.
Sports landing manoeuvres
Bending the knees when jumping down from a high place is a natural movement to disperse the impact loads.
5. summary.
Impact loading is a temporary large force that occurs when an object is subjected to acceleration. When you jump on a scale, the needle shakes a lot, which is also caused by this shock load phenomenon.
By learning about the principles of mechanics from familiar phenomena, you may find the world of physics a little more familiar! Next time you use the scales, don't just get on gently, try jumping on them (safely!). It might be interesting to experience this phenomenon for yourself.
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