Grade 12 Physics Concepts: Impulse
The formula for impulse is written as FΔt=Δp where F is force acting on an object, Δt is time the force is acting on an object and Δp is change in momentum. Since FΔt represents Impulse and Δp a change of momentum, impulse is equal to the change in momentum. According to this formula, the force an object experiences decreases if the time a force has to change its momentum increases. This property forms the basis of many tecnologies that keep people safe during car crashes such as air bags, crumple zones, crash cushions , seatbelts and break away utility poles, since they all increase the amount of time an object is colliding.
Figure 1: Shows how the formula for impulse is derived. The formula for force is first taken and then acceleration is subbed in with v/t from the five motion equations. This thereby results in FΔt=mΔv which can be rewritten as FΔt=Δp, since p=mΔv.
Figure 2: Shows various values of Force and Time possible when an Impulse of zero is present. The decreasing values of force in correspondence to increasing values of time show the directly proportional relationship between force and time.
Figure 2 reveals something important to note about the relationship between force and time. The greater the time during which a collision occurs, the smaller the force acting on an object. Therefore, to minimize the force acting on an object involved in a collision, the time must be increased. And to maximize the effect of the force on an object involved in a collision, the time must be decreased. Many important car saftey features are engineered with this feature of impulse in mind.
