P4 Key Facts Flashcards
what is displacement?
when distance is given with a particular indication of direction
If an object is placed on a table, which equal force acts against the objects weight?
The reaction force
If a car or plane is moving what are the forces acting on it?
an equal weight and reaction force
Equal thrust force(from engine) and drag force (from air resistance)
what is a resultant force?
the overall force acting on an object (add up all the forces)
What does the resultant force decide?
it decides the motion of the object (whether it accelerates, decelerates or stays at a steady speed)
What is momentum?
How hard it would be to stop an object moving (dependant on the weight and speed of the object)
Momentum equals mass multiplied by velocity
What happens when a resultant force acts on an object?
It causes a change in momentum in the direction of the force
what happens if someones momentum changes very quickly?
the forces acting on the body will be large which makes them more likely to cause injury
This is because the quicker you come to a complete stop the greater the force and the greater the damage
Which features of a car act in increasing the collision time and reducing the forces on the passengers?
crumple zones, air bags, seat belts and helmets (bikes)
What is work done (in joules)?
the energy transferred when a force moves an object (force x distance)
what is kinetic energy?
the energy that anything moving gains (the greater the mass of the object the faster it goes and the bigger its kinetic energy)
how do you increase kinetic energy?
By increasing its velocity (done by applying a force)
However because kinetic is just movement of energy, if you do work on a object but it doesn’t actually move, then its kinetic energy doesn’t increase
How is energy always conserved?
energy never goes away, it just gets transformed from one type of energy to another (e.g electrical into light and heat)
why is the increase in an objects kinetic energy normally a bit less than the amount of work done on it?
some energy is wasted as heat due to forces such as air resistance and friction
what is gravitational potential energy (GPE)
the energy stored in an object when you raise it to a height against the force of gravity (if you raise an object its GPE increases and if the object falls the GPE decreases)
