Difference between revisions of "Impact Force"
(Created page with "==Key Stage 4 Higher== ===Meaning=== An '''impact force''' is the force involved in the collision between two objects. ===About Impact Forces=== : '''Impact forces'''...") |
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===Equation=== | ===Equation=== | ||
''NB: You do not need to remember the equation but you do need to be able to use it. | ''NB: You do not need to remember the equation but you do need to be able to use it. | ||
| − | Combining the two equations | + | Combining the two equations |
| − | <math>a=\frac{F}{m}</math> | + | <math>a = \frac{F}{m}</math> |
and | and | ||
| − | <math>a = \frac{\ | + | <math>a = \frac{\Delta v}{t}</math> or <math>a = \frac{v-u}{t}</math> |
Gives | Gives | ||
| − | <math>\frac{F}{m} = \frac{\ | + | <math>\frac{F}{m} = \frac{\Delta v}{t}</math> |
| − | <math>F = \frac{m \ | + | <math>F = \frac{m \Delta v}{t}</math> or <math>F = \frac{mv - mu}{t}</math> |
| − | Where | + | Where |
| − | <math>F < | + | <math>F </math> = The impact [[force]]. |
| − | <math>m \ | + | <math>m \Delta v</math> = The change in [[momentum]]. |
| − | <math>t< | + | <math>t</math> = The time taken for the [[momentum]] to change. |
| + | |||
| + | <math>m</math> = The [[mass]] of the [[object]]. | ||
| + | |||
| + | <math>mv</math> = The final [[momentum]] of the [[object]]. | ||
| + | |||
| + | <math>mu</math> = The initial [[momentum]] of the [[object]]. | ||
| + | |||
| + | ===Example Calculations=== | ||
| + | {| class="wikitable" | ||
| + | | style="height:20px; width:300px; text-align:center;" |A car travelling at 20m/s collides with a lamppost and comes to a complete stop in 0.16 seconds. If the passenger has a [[mass]] of 80kg, calculate the [[force]] exerted by the seat belt on the passenger correct to two [[Significant Figures|significant figures]]. | ||
| + | | style="height:20px; width:300px; text-align:center;" |During a crash the air bag activates. By the time the car stops the drivers 5kg head is still moving forward with a velocity of 2.4m/s and collides with the airbag. This collision lasts for 0.25 seconds. Calculate the [[force]] between the air bag and the person's head during the collision. | ||
| + | |- | ||
| + | | style="height:20px; width:300px; text-align:left;" |'''1. State the known quantities''' | ||
| + | |||
| + | Δv = 20m/s | ||
| + | |||
| + | t = 0.16s | ||
| + | |||
| + | m = 80kg | ||
| + | | style="height:20px; width:300px; text-align:left;" |'''1. State the known quantities''' | ||
| + | |||
| + | Δv = 2.4m/s | ||
| + | |||
| + | t = 0.25s | ||
| + | |||
| + | m = 5kg | ||
| + | |- | ||
| + | | style="height:20px; width:300px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers into the [[equation]] and [[Solve (Maths)|solve]].''' | ||
| + | |||
| + | <math>F = \frac{m \Delta v}{t}</math> | ||
| + | |||
| + | <math>F = \frac{80 \times 20}{0.16}</math> | ||
| + | |||
| + | <math>F = \frac{1600}{0.16}</math> | ||
| + | |||
| + | <math>F = 10000N</math> | ||
| + | | style="height:20px; width:300px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers into the [[equation]] and [[Solve (Maths)|solve]].''' | ||
| + | |||
| + | <math>F = \frac{m \Delta v}{t}</math> | ||
| + | |||
| + | <math>F = \frac{5 \times 2.4}{0.25}</math> | ||
| + | |||
| + | <math>F = \frac{12}{0.25}</math> | ||
| + | |||
| + | <math>F = 48N</math> | ||
| + | |} | ||
Latest revision as of 20:41, 5 January 2020
Contents
Key Stage 4 Higher
Meaning
An impact force is the force involved in the collision between two objects.
About Impact Forces
- Impact forces are proportional to the change in momentum during a collision and inversely proportional to the time taken for the collision.
- Impact forces explain the reason crashing at high speed is so dangerous and why cars have crumple zones and air bags. They both increase the time taken for the passengers to change momentum which reduces the force experienced by them.
Equation
NB: You do not need to remember the equation but you do need to be able to use it. Combining the two equations
\(a = \frac{F}{m}\)
and
\(a = \frac{\Delta v}{t}\) or \(a = \frac{v-u}{t}\)
Gives
\(\frac{F}{m} = \frac{\Delta v}{t}\)
\(F = \frac{m \Delta v}{t}\) or \(F = \frac{mv - mu}{t}\)
Where
\(F \) = The impact force.
\(m \Delta v\) = The change in momentum.
\(t\) = The time taken for the momentum to change.
\(m\) = The mass of the object.
\(mv\) = The final momentum of the object.
\(mu\) = The initial momentum of the object.
Example Calculations
| A car travelling at 20m/s collides with a lamppost and comes to a complete stop in 0.16 seconds. If the passenger has a mass of 80kg, calculate the force exerted by the seat belt on the passenger correct to two significant figures. | During a crash the air bag activates. By the time the car stops the drivers 5kg head is still moving forward with a velocity of 2.4m/s and collides with the airbag. This collision lasts for 0.25 seconds. Calculate the force between the air bag and the person's head during the collision. |
| 1. State the known quantities
Δv = 20m/s t = 0.16s m = 80kg |
1. State the known quantities
Δv = 2.4m/s t = 0.25s m = 5kg |
| 2. Substitute the numbers into the equation and solve.
\(F = \frac{m \Delta v}{t}\) \(F = \frac{80 \times 20}{0.16}\) \(F = \frac{1600}{0.16}\) \(F = 10000N\) |
2. Substitute the numbers into the equation and solve.
\(F = \frac{m \Delta v}{t}\) \(F = \frac{5 \times 2.4}{0.25}\) \(F = \frac{12}{0.25}\) \(F = 48N\) |