Topic 5 - Forces Flashcards
What is a Moment?
A moment is a turning force, it causes rotation.
What is equilibrium?
In terms of forces.
Equilibrium is when there is no net moment - the anti-clockwise moment = the clockwise moment.
What is the equation for a moment?
Moment = Force x perpendicular distance from pivot to line of action of the force.
M = F x d
What is a lever?
A lever is a force multiplier, the longer the lever, the greater the force.
What is effort?
Effort is the force applied to something like a lever.
What are gears?
Gears are components which transfer rotational force from one area to another.
What is a fluid?
Any substance that can flow
What is the equation for pressure?
Pressure = Force/Area
p =F/A
What causes gas pressure?
Everytime particles hit the side of a container, the particles exert a force at right angles to the container walls.
What is the unit for pressure?
Pascals or N/m
What is upthrust?
the upward force that a liquid or gas exerts on a body floating in it.
What causes upthrust?
upthrust exists because the pressure at the top of an object is less than the pressure at the bottom of an object.
What is upthrust equal to?
Upthrust is equal to the weight of the fluid displaced by an object.
What determines if an object can float?
It’s density - if the density is higher than the fluid it’s in, it will sink.
Vice versa.
What is Distance Vs Displacement?
Distance - How far you have gone(scalar)
Displacement - How far you have gone from you start point with direction.(Vector)
What are scalars?
Scalars are quantities which have magnitude
What are vectors?
Vectors are quantities which have a magnitude and direction
What are the 6 typical values of speed
1.walking - 1.5m/s
2.running - 3m/s
3. Cycling - 6m/s
4. Car - 25m/s
5. Train - 55m/s
6. Plane - 250m/s
What is the difference between speed and velocity?
Speed is a scalar, velocity is a vector
In free body diagrams, where should weight be drawn from?
The centre of gravity
What is the technique for scale drawings?
- Pick a suitable scale
- Tip-to-tail rule
- Do a rough sketch
What does resolving forces mean?
Resolving forces are when a resultant force is split into its 2 component vectors, vertical components and horizontal component.
What does equilibrium mean?
No net force.
What is the equation for work done?
Work don = force x distance moved in direction of force
W = F x s
What is an elastic object?
An elastic object is one which returns to its original shape and size, when the force is removed. Up to a limit of proportionality
What is Hooke’s law?
Hooke’s law stated that the extension for any elastic object is directly proportional to the force applied. Provided the limit of proportionality is not exceeded.
What is the equation for elastic potential energy?
Ep = 1/2ke^2
What 2 factors affect top speed?
- Streamline
- Power
What is Newtons first law?
An object will remain at constant speed or at rest, unless a resultant force acts on it
What is Newtons 2nd law
Objects will accelerate in the direction of a resultant force
What is the equation linking force, mass and acceleration
Force = mass x acceleration
F = m x a
What is inertia?
Inertia is the reluctance of an object to change its state of motion.
What is stopping distance?
Braking distance+thinking distance
What factors affect thinking distance?
1.alcohol/drugs
2.tiredness
3.speed
4.age
What are some examples of vector quantities?
- Force
- Velocity
- Displacement
- Acceleration
- Momentum
What are some examples of scalar quantities?
- Speed
- Distance
- Mass
- Temperature
- Time
What is an interaction pair?
A pair of forces that are equal and opposite and act on two interacting objects.
What is the equation linking Force, mass and gravity?
Force = mass x gravitational field strength
F=mg
What is the relationship between joules and newton metres?
1 Joule = 1 Newton metre
1J = 1Nm
What is the equation linking pressure, height, density and GFS?
Pressure = height x density x gravitational field strength
p = hρg
What is Newton’s 3rd law?
When 2 objects interact, the forces they exert on eachother are equal and opposite
What is a system?
A group of objects which interact
What are the 2 suvat equations?
- a=(v-u)/t
acceleration= (final - initial velocity)/time - a=(v^2-u^2)/2s
acceleration= (final^2-initial^2)/2s
What factors affect braking distance?
1.speed
2.condition if brakes/tyres
3.wet/icy roads
4.mass
How is speed related to thinking distance?
Thinking distance is directly proportional to the scale factor of the speed increase
How does braking distance change with speed?
It increases with the square of the scale factor of the speed increase
What is the equation for momentum?
momentum = mass x velocity
p = m x v
What is the law of conservation of momentum?
In a closed system, the total momentum before a collision or explosion is equal to the total momentum after.
What is the equation linking force, momentum and time?
force = change in momentum/time
F = Δp/t
What are 3 components of car safety?
- seat belt
- airbags
- crumple zones
What do seat belts do in an impact?
- made of elastic material, so it stretches
- thus increasing the time of impact
- so less force is transfered to the passenger
What do airbags do in an impact
sensors in the bumper detect a collision, which causes an explosion, inflating the airbag, this increases the time of the impact.
What do crumple zones do in an impact?
Deforms and breaks on impact, thus increasing the time of collision
How much momentum is there before an explosion?
NONE
