P8 - Forces Flashcards
Size of force is measured in:
Newtons (N)
Hooke’s law:
The extension of a piece of wire is directly proportional to the applied force providing the limit of proportionality is not exceeded.
To calculate weight:
Mass x acceleration due to gravity.
To find the density:
Mass / volume
What is inertia
The tendency of an object to resist a change in speed caused by force, directly related to its mass.
Objects with larger mass have larger inertia meaning it is more difficult to speed up or low down.
This is a factor in the need for seat belts, as our bodies take time to change velocity.
Balanced forces occur when:
There is equal force acting in both directions on an object.
Can cause it to remain stationary or continue to move in the same direction at a constant speed.
When does terminal velocity occur?
When there is no resultant force, and the object moves at a constant speed.
How is slow down and stop achieved in a car?
- The driver removes foot from the accelerator to reduce the driving force from the engine.
- He applies the brakes, which increases friction between the road and the car tyres.
The minimum stopping time after brakes have been applied depends on:
- Thinking time (how long it takes for driver apply brakes)
- The surface conditions of the road
- The speed of the car before braking.
To work out stopping distance on a dry road:
Thinking distance - 9m
Braking distance - 14m
Stopping distance = t + b
9 + 14 = 23m
To work out work done:
Force x distance moved
Where is the centre of mass on a regular object?
At its geometric centre.
When will an object be stable?
When the vertical line from its centre of mass is inside the base of the object.
If an object has neutral stability:
Their centre of mass is always directly above their base. They stay where they are tilted and don’t return to the original position or topple over.
E.g. Cylinders or spheres.
Scalar:
Measured quantities that only indicate one size or magnitude
E.g. Speed, only indicates how fast an object is moving.
