Impulse

Definition of Impulse

  • Impulse is a vector quantity that represents the change in an object’s momentum.
  • The term is often used to link momentum and the forces acting on an object over a period of time.
  • The impulse experienced by an object is effectively the impact of a force on that object.
  • Impulse can be calculated from J = FΔt, where J represents Impulse, F is the force applied, and Δt is the duration of time for which the force is applied.

Properties of Impulse

  • Being a product of force and the time interval during which the force acts, impulse has both a magnitude (the overall effect of the force and the time) and a direction, which is determined by the force’s direction.
  • Impulse, like momentum, has units of kg m/s (kilogram metre per second). Alternatively, it can also be expressed in N s (Newton seconds), where a Newton second is a derived SI unit equal to a kilogram metre per second.

Impulse-Momentum Theorem

  • The impulse-momentum theorem states that the change in momentum of an object equals the impulse acted on it. Simply, FΔt = Δ(mv).
  • This concept forms the basis for understanding how forces affect the motion of objects. It says that if an external force is applied to a system, the momentum of that system changes.
  • Impulse-momentum theorem is particularly useful in collision and explosion scenarios; for both elastic and inelastic collisions, the concept of impulse can be used to work out the resultant velocities of the involved objects.

Applications of Impulse

  • Understanding impulse is vital in many real-world situations such as car safety designs. For instance, crumple zones in cars are designed to increase the collision time, thereby reducing the impact force. More time for the force to act results in smaller forces experienced, preventing severe injury to the occupant.
  • Similarly, a cricketer or a goalkeeper will often be seen “pulling” their hands back after catching. This technique increases the time over which the force due to the ball acts - reducing the magnitude of the force, thereby making the catch less painful.
  • Concepts of impulse also help understand physical activities like jumping on a trampoline or how airbags work in protecting drivers in car crashes.
  • It also plays a crucial role in the successful launch of rockets into space, as the magnitude of thrust required is directly related to the impulse.