Chapters 5-7 Flashcards
Moment of a force =
Force x perpendicular distance of the pivot from the line of action of the force
Define centre of gravity?
The point through which the entire weight of the object maybe be considered to act.
What is the principle of moments?
For any object that is in equilibrium, the sum of clockwise moments about a point is equal to the sum of the anticlockwise moments about that same point.
What is a couple?
A pair of equal and opposite forces that are not acting in the same straight line.
Define torque?
The product of one of the forces of a couple and the perp distance between them (Nm).
Torque of a couple =
One of the forces x perpendicular distance between the two forces.
When is the equilibrium of a body achieved?
When the resultant force and resultant torque on the body are both zero.
Density =
Mass/volume
Define pressure?
The normal force per unit cross sectional area.
Pressure =
Normal force / cross sectional area
N/m^2
Define thinking distance?
The distance travelled by the car in the time the driver reacts to a particular situation.
Define braking distance?
The distance travelled by the car as the brakes are engaged and the car comes to a stop.
Define stopping distance?
Thinking distance + braking distance
Power = ?
Rate at which energy is transferred or rate at which work is done.
P=work(j)/time(s)
Work done =
Displacement in direction of force x force
What is a joule?
Energy transferred when a force of 1N moves a distance of 1m in the direction of the force
GPE =
Mgh
KE =
0.5x m x v^2
What does the principle of conservation of energy state?
That for a closed system, energy can be transformed to other forms but the total amount of energy remains constant.
Efficiency =
Useful output energy / total input energy x100
What is a watt?
A transfer of energy of one joule per second.
Explain how crumple zones help to make cars safer?
Front and rear crumple zones mean that if the car crashes, they squash up, and therefore absorb a lot of the energy from the impact. This means that less of the energy reaches the passengers and so they are safer.
Explain how seat belts help to keep passengers safe?
When a car crashes or stops suddenly, the car will stop but the people inside will keep on moving forwards, possibly into the windscreen or steering wheel. Seat belts hold passengers onto their seats so this doesn’t happen. They are also slightly stretchy so the passenger isn’t brought to a halt too suddenly. Finally, they extend across the whole torso so that the pressure of the seatbelt on the body is spaced out rather than being confined to one small space on the body.
Explain how air bags help to keep people safe?
If a car suddenly decelerates, the air bag will inflate so that as the person moves forward they are cushioned as they move forwards. It stops them hitting the windscreen/steering wheel. There are holes in the bag so that it deflates quickly after being inflated to prevent the person from bouncing back off the airbag.
