Dynamics Flashcards
Define mass
Mass is a property of a body which resist change in motion.
Define momentum
Momentum of a body is the product of its mass and velocity of a moving body.
Define Newton’s First Law
Newton’s first law of motion states that in the absence of resultant force, a body at rest will remain at rest and a body in motion will continue in motion at constant velocity.
Define Newton’s Second Law.
Newton’s Second Law of motion states that the rate of change of momentum of a body is proportional to the resultant force acting on the body, and the momentum change takes place in the direction of resultant force.
What is the relationship between impulse and change in momentum?
impulse=change in momentum
Define impulse
Impulse of a force is the product of average force and the time during which it acts.
What is apparent weight?
Apparent weight is the force exerted on the object by the body that is freely supporting it.
What is the apparent weight of a free falling body?
zero
Define the Principal of Conservation of Momentum
When bodies in a system interact, the total momentum remains constant provided no resultant external force acting on the system.
Define elastic collision
Elastic collision is one in which the total kinetic energy is the same before and after the collision.
What happens during a head on elastic collision?
relative speed of approach before collision=relative speed of separation after collision
(use when mass is not given)
What are the 3 equations that apply to elastic collision?
- Conservation of momentum
- Conservation of KE
- Relative speed of approach=relative speed of separation
Define inelastic collision
Inelastic collision is one of which the total kinetic energy is not the same before and after the collision.
Define a completely inelastic collision
It is one in which the bodies move together with the same velocity after collision.
What is superelastic collisions?
It is where kinetic energy is gained after the collision.
What does it meant by a head on collision?
The velocity vectors of the colliding bodies before and after the collision are along the line joining their centre of mass.
What does it mean by the total reaction force of a body?
It is the vector sum of the normal reaction force and frictional force acting on the body.
What are the 3 kinds of resistance force?
- static friction
- kinetic friction
- viscous force (of liquid/gas)
What are the contact forces?
- Frictional force
- Normal contact force
- Tension/ Compression of string,spring or rod
- Upthrust (acts at the centre of mass of displaced fluid)
- Lift
- Thrust
What direction does lift act?
Lift act in the direction perpendicular to the relative flow of surrounding fluid
What are the 3 car safety features?
- front and rear crumple zones
- seatbelts
- airbags
How does the front and rear crumple zones protect passengers during a car crash?
It will collapse during a collision which allows the change in momentum of passengers to take place over a longer time interval, hence reducing the impact force in passenger.
How does airbags protect the driver?
It inflates very quickly during a collision and they provide a softer surface to prevent people from hitting hard objects
How does seatbelts protect people during a collision?
- It prevents the person from being thrown around in the car,possibly through the windscreen or hitting themselves on the steering wheel or other objects.
- The seatbelt also stretches a little, while restraining the person during a crash. The stretching increases the amount of time it takes the person to stop.
