topic 5: forces Flashcards
6 examples of scaler quantities
mass temperature speed energy distance time
what is scaler and vector
scaler-just magnitude no distance
vector-magnitude and distance
name 6 vector quantities
displacement weight force velocity acceleration momentum
what is a force
A force is a push or pull that acts on an object due to the interaction with another object
is force vector or scaler
vector
name contact forces
tension,friction,air resistance
normal contact force-(lamp) the lump is exerting a downward force on the table which is the weight 
name non contact force
gravitational force,electrostatic force,magnetic force
what is the weight of an object
The weight of an object is the force acting on it due to gravity
newtons
what is weight equation
weight (N) = mass (kg) x gravitational field strength (N/kg)
what is the centre of mass
The weight of an object can be considered to act a singular point
how can a vector quantity be drawn and what does it show?
As an arrow
The length of the arrow represents the magnitude
The arrow points in the associated direction
what is a force? 
A push or a pole acting on an object due to an interaction with another object
give three examples of vector quantities
Velocity
Displacement
Force
What is weight?
The force that act on an object due to gravity and the object mass
What is meant by an object centre of mass?
The single point where an object weight can be considered to act through
what piece of equipment can be used to measure objects weight?
A calibrated spring balance or Newton meter
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 does it mean if a force is said to do work?
The force causes an object to be displaced through a distance
what distance must be used when calculating work done?
It must be the distant that is moved along the line of action of the force
What occurs when Work has done against frictional forces
A rise in temperature of the object occurs
Kinetic energy is converted to heat
Why does air resistance slow down a projectile?
The object does work against the air resistance
Kinetic energy is converted into heat, slowing down the object
explain the relationship between the force supplied 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 an inelastic deformation?
A deformation which results in the object being permanently stretched
The object doesn’t return to its original shape when the force is removed
What can extension be replaced with in the equation for spring force?
Compression
what is an alternative name for the turning effect of a force?
A moment
What distant measurement is used when calculating the 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 moment acting on the object?
The clockwise moments are equal to the anticlockwise moments
what 3 parts make up a lever system?
load
effort
pivot
How can a lever be used as a force multiplier?
If the distance between the effort and the pivot is greater than the distance between the pivot and the load, the force applied on the load is greater than the effort force. This is since the moment on both the effort and load must be the same.
give an example of when a lever may be used to multiply a force
A wrench, which has a long handle also that the force supplied 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 year being driven by a smaller gear
The larger wheel will rotate more slowly, but will also produce a larger moment
what is meant by the term fluid?
A liquid or a gas
in any fluid at what angle did the forces due to pressure act on a given surface
At right angles
what happens to the density of the atmosphere when increasing altitude
The atmosphere becomes less dense as altitude increases
explain why atmospheric pressure decreases with an increase in height
Pressure is created by collisions of air molecules
The quantity of molecules decreases as the height increases
This means atmospheric pressure decreases with an increase of hight
What is the earths atmosphere?
A thin (relative to the magnitude of the Earth) layer of gas surrounding the Earth
how does pressure in fluids increase with depth
As the depth increases, the mass of liquid above that depth of so 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?
 density of fluid increases the number of particles in a given volume increases. Consequently the weight of the fluid is greater. This means that the fast from the fluid above the certain point is larger. Since the force has increased, blood pressure also increases.
why are objects in a fluid subject to a 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 the top. This leads to an upwards force called upthrust. You float or sink depending on whether upthrust is more or less than your weight. 
what is upthrust always equal to?
The weight of the fluid that the object displaces
what factors influence whether an object will sink or float?
upthrust
weight
density of fluid
explain why an object with a density greater than 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 objects weight 
does a distance quantity require a specific direction i.e. is a scaler or vector quantity
No specific direction is required so it is a scaler quantity
if an object moves 3 m to the left and then 3 m back to its initial position, what is the object total displacement?
The object has zero displacement
Displacement is a vector quantity, so it also involves direction
The object starts and ends at the same point
State a typical value for the speed of sound
330 m/s
What is a typical value for the human walking speed?
1.5m/s
what is the typical value of human running speed?
3 m/s
What is the typical value for human cycling speed?
6 m/s
Why can I object travelling at a constant speed in a circle not have a constant velocity?
speed is a scaler quantity
Velocity is a vector quantity which means it can only be constant if the direction is constant
In a circular motion, the direction is continuously changing
how can speed be calculated from a distant 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 distant time graph for an accelerating object
Drawing a tangent to the curve at the required time
Calculating the gradient of the tangent
how can the distant travelled by an object to be calculated from a velocity time graph
It is equal to the area under the graph
What can be said about the resultant force acting on an object when it is falling at terminal velocity?
The resultant force is zero
When at terminal velocity the object is moving at a constant speed and so isn’t accelerating
State Newton’s first law for a stationary object
If the result of force on a stationary object is zero, the object will remain at rest
State Newton’s first law for a moving object
If the result on force on a moving object is zero, the object will remain at a constant velocity
what can be said about the breaking forces and driving forces when a car is travelling at constant velocity?
The breaking forces are equal to the driving forces
if an object changes direction but remains at constant speed, is there a resultant force?
Since there is a change in direction, there is a change in velocity and so there must be a resultant force
what is inertia
The tendency of an object to continue in its state of rest or uniform motion
State Newton second law in words
An object acceleration is directly proportional to the resultant force acting on it and inversely proportional to its mass
what is inertial mass
A measure of how difficult it is to change a given object velocity
The ratio of force over acceleration
State Newton’s third law
Whenever two objects interact, the fastest that they expert on each other are always equal and opposite
what is the stopping distance for a vehicle equal to
The sum of thinking distance and breaking distance
forgiven breaking distance, if the vehicle speed is increased, what can be said about it stopping distance?
The stopping distance is increased with an increase in speed
give a typical range of values for human reaction time
0.2–0.9 seconds
Give free factors which can affect a drivers reaction time
tiredness
Drugs
alcohol
Give two factors which may affect breaking distance
adverse road conditions
Poor tire/brake conditions
describe the energy transfers that take place when a car applies its brakes
Work is done by the friction force between the brakes and wheel
Kinetic energy of the wheel is converted to heat and is dissipated to the surrounding through the brake discs
To stop a car in a given distant, if it’s Lotti is increased, what must happen to the breaking force applied
The breaking force must also be increased
State to consequences of a vehicle undergoing very large decelerations
kinetic energy converted to heat is very high causing brakes to overheat
Loss of control of the vehicle
In a close system, what can be said about the momentum before and after collision?
The total momentum before is equal to the total momentum afterwards
what quantity is equal to the force experience in a collision?
The rate of change of momentum
if an object change of momentum is fixed, what is the only way to reduce the force that the object experiences?
Increase the length of time over which the change of momentum occurs
Explain how a seatbelt improves a passenger safety during a collision
passengers must deaccelerate from the vehicles velocity at impact to 0, meaning they undergo a fixed change of momentum
The first experience is equal to the rate of change of momentum
Seatbelts increase the time over which the force is applied, reducing the rate of change of momentum and therefore reducing the force experienced
