forces Flashcards
what is a scalar quantity?
a quantity that only has a magnitude, it is direction dependent
what is a vector?
a quantity has both an associated direction and magnitude
How can a vector quality be drawn and what does it show?
- an arrow
- the arrow points in certain directions
- the length of the arrow represents the magnitude
what is a force
a push or pull acting on an object due to an interaction with another object
what are the two forces categories
- non-contact forces
- contact forces
3 examples of contact forces
- friction
- air resistance
- tension
3 examples of non-contact forces
- gravitational forces
- electrostatic forces
- magnetic forces
is force a vector or a scalar quantity
- vector
- it has a magnitude and an associated direction
3 examples of a vector quantity
- velocity
- displacement
- force
examples of scalar quantities
- temp
- time
- mass
- speed
- distance
- energy
what is weight
the force that acts on an object due to gravity and the objects mass
weight equation
weight = mass x gravitational field strength
unit for weight
Newton (N)
unit for gravitational field strength
N/Kg
what is meant by an objects centre of mass
the single point where an objects weight can be considered to act through
what is the name given to the single force that is equivalent to all the other forces acting on a given object
the resultant force
what is the equation used to calculate work done?
work done = force x distance
what distance must be used when calculating work done
the distance that is moved along the line of action of the force
what occurs when work is done against frictional forces
- rise in temp
- kinetic energy is converted to heat energy
explain the relationship between the force applied and the extension of an elastic object
the extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded
what is meant by inelastic deformation?
- a deformation which results in an object being permanently stretched
- the object does not return to its original shape when force is removed
state the equation relating force, spring constant, extension
force = spring constant x extension
what type of energy is stored in a spring when its stretched
elastic potential energy
what is an alternative name for the turning effect of a force
a moment
state the equation to calculate the moment of a force
moment of a force = force x distance
what distance measurement is used when calculating a moment
the perpendicular distance from the pivot to the line of action of the force
if an object is in equilibrium, what can be said about the moments acting on a force
the clockwise moments are equal to the anticlockwise moments
3 parts of lever system
- load
- pivot
- effort
how can a lever be used as a force multiplier
if the distance between the effort and pivot is greater than the distance between the pivot and load, the force applied on the load is greater than the effort force. this is since the moment on both the effort and the load must be the same
example of when a lever may be used to multiply a force
a wrench
it has a long handle so that the force applied by the user is multiplied
what determines the moment of a gear wheel
the size of the wheel
describe the moment and speed of a larger gear being driven by a smaller gear
the larger wheel will rotate more slowly but will also produce a larger moment
does a distance quantity require a specific distance
no specific distance is needed
so it is a scalar quantity
typical value for speed of sound
330 m/s
typical value for human walking speed
1.5m/s
typical value for human running speed
3 m/s
typical value for human cycling speed
6 m/s
equation that links speed, distance and time
distance = speed x time
why can an object travelling at a constant speed in a circle not have a constant velocity
- speed is a scalar quantity
- velocity is a vector quantity which means it can only be constant if the direction is constant
- the a circular motion, the direction is constantly moving
how can speed by calculated from a distance-time graph
the speed is equal to the gradient of the graph
what must be done to calculate speed at a given time from a distance-time graph from a accelerating object
- draw a tangent to the curve at the required time
- calculating gradient of the tangent
equation for average acceleration of an object
acceleration = change in velocity / time taken
how can the distance travelled by an object be calculated from a velocity time graph
it is equal the the area under the graph
approx value for the acceleration of an object in free fall under gravity (earth surface)
9.8 m/s(squared)
what can be said about the resultant force acting on an object when it is falling at terminal velocity
- resultant force is zero
- what at terminal velocity, the object is moving at a constant speed and so isn’t accelerating
state newtons first law of motion
every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force.
what can be said out the braking forces and driving forces when a car is travelling at constant velocity
the braking forces are equal to the driving forces
what is inertia
the tendency of an object to continue its state of uniform motion or rest
equation for newtons 2nd law of motion
resultant force = mass x acceleration
newtons 2nd law of motion
an objects acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass
what is inertia mass
- a measure of how difficult it is to change a given objects velocity
- the ratio of force over acceleration
newtons 3rd law of motion
His third law states that for every action (force) in nature there is an equal and opposite reaction.
what is the stopping distance of a vehicle equal to
sum of thinking distance and braking distance
for braking distance:
if the vehicle speed increased what would happen to the stopping distance
the stopping distance is increased with an increase in speed
3 factors which effect drivers reaction time
- tiredness
- drugs
- alcohol
2 factors which effect braking distance
- road conditions
- poor tyre brake conditions
describe the energy transfers that take place when a car applies its breaks
- work done by the friction between brakes and wheel
- kinetic energy of wheel is converted to heat and is dissipated to the surroundings through brake discs
To stop a car in a given distance if it’s velocity is increased, what must happen to the braking force is applied
The braking force must also be increased
State 2 consequences of a vehicle undergoing very large decelerations
- Kinetic energy converted to heat is very high causing brakes to overheat
2 loss of control of the vehicle
equation for pressure
pressure = force / area
equation for pressure in a fluid column
pressure = height of fluid above the point x density x field strength
what is meant by fluid
a liquid or a gas
what happens to the density of the atmosphere with increasing altitude
the atmosphere becomes less dense as altitude increases
how does pressure in fluids increase with depth
as the depth increases, the mass of liquid above that depth also increases. this means that the force due to the mass increases. since the force has increased whilst the area has remained constant, the pressure will increase
why does pressure in fluids increase with density
as the density of a fluid increases, the number of particles in a given volume increases. consequently the weight of the fluid is greater, the means that the force from the liquid above a certain point is larger. since the force has increased, the pressure also increased
why are objects in a fluid subject to an upthrust?
when an object is submerged in a fluid, it has a higher pressure below it then it does above, as there is more weight above it at the bottom than there is at the top. this leads to an upwards force called up thrust. you float or sink depending on weather the up thrust is more or less your weight
what is upthrust always equal to
the weight of the fluid that the object displaces
factors that will influence whether an object will sink or float
- upthrust
- weight
- density of fluid
explain why an object with a density greater than that of water can never float
upthrust is equal to the weight of the displaced fluid. if the density of the object is high, there would not be enough volume displaced to produce an upthrust larger than the objects weight. it will sink
