Dynamics Flashcards
chapter 3 (16 cards)
Define mass
Mass is the property of a body which resists change in motion (inertia).
Define momentum
The linear momentum of a body is defined as the product of its mass and its velocity.
(p=mv)
Newton’s First Law of Motion
In the absence of resultant force acting on it, a body at rest will remain at rest and a body in motion will continue in motion at constant velocity.
Newton’s Second Law of Motion
The rate of change of momentum of a body is proportional to the resultant force action on the body, and the momentum change takes place in the direction of the resultant force.
Newton’s Third Law of Motion
When body A exerts a force on body B, body B exerts a force of equal magnitude but opposite in direction on body A.
(they arise from same type of interaction and they act on different bodies)
Define impulse
The impulse of a force is the product of the average force and the time during which it acts.
Explain safety feature of front and rear crumple zone of car
The car is designed so that the structure of the car will give way during a collision. The metal of the car will dent, bend and fold during a collision which increases the amount of time it takes the car to stop.
Explain safety feature of seatbelts of car
two ways:
The seatbelt prevents the person being thrown about in the car, possibly through the windscreen or hitting themselves on the steering wheel or other objects.
The seatbelt also stretch a little, while restraining the person during a crash. The stretching increases the amount of time it takes the person to stop.
Explain the safety feature of airbag in the car
Airbag will inflate very quickly during a crash, they provide a softer surface to prevent the people hitting themselves on hard objects. It will give way a little when a person hits it and this gives an extra increase to the amount of time it takes the person to stop.
Define weight
The weight of an object is the gravitational force exerted on the object by the earth.
Principle of Conservation of Linear Momentum
When bodies in a system interacts, the total momentum remains constant provided no resultant external force acts on the system.
(initial p = final p)
Define head-on collision
The velocity vectors of the colliding bodies before and after the collision are along the lines joining their centres of mass.
Relative speed of approach before the collision equal to relative speed of separation after the collision
( u₁ - u₂ = v₂ - v₁ )
Define elastic collision
An elastic collision is one in which kinetic energy is conserved.
( total ke before = total ke after)
Define inelastic collision
An inelastic collision is one in which kinetic energy is not conserved.
( initial ke > final ke )
Define completely inelastic collision ( Perfectly inelastic collision)
A completely inelastic collision is one in which the bodies join together (coalesce) after collision.
Define superelastic collision
A superelastic collision is one in which kinetic energy is gained.
( initial ke < final ke )
