Forces Flashcards
To revise forces (Paper 2)
Define a scalar
A quantity that only has magnitude.
Give some examples of scalar quantities
Speed, distance, time, mass, volume
Define a vector quantity
A quantity that has magnitude and direction.
Give some examples of vector quantities
Velocity, displacement, acceleration, momentum, any force
State some examples of contact forces
Friction, air resistance, drag, upthrust, tension, normal contact force
State some examples of contact forces
Gravity, magnetism, electrostatic
State the equation with all units for Weight
weight (N) = mass (kg) × gravitational field strength(N/kg)
What is the mathematical relationship between weight and mass.
They are directly proportional
What equipment can be used to measure weight?
Weight is measured using a calibrated spring-balance called a newtonmeter
Define a resultant force
When a number of forces acting on an object may be replaced by a single force that has the same effect as all the original forces acting together.
When is work done?
When a force causes an object to move through a distance
What is the relationship between work done and energy transferred
Work done = energy transferred
State the equation and all units for work done
work done (J) = force (N) × distance moved along the line of action of the force (m)
Define 1 joule of work
One joule of work is done when a force of one newton causes a
displacement of one metre. 1 joule = 1 newton-metre
State Hooke’s law
The extension of an elastic object, such as a spring, is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.
State Hookes law equation with all units
force (N) = spring constant (N/m) × extension (m)
When an object is stretched or squared what form of energy does it store?
Elastic potential energy.
Define elastic deformation
When the forces are removed the object returns to its original length
Define inelastic deformation
When the forces are removed the object doesn’t returns to its original length, it stays permanently stretched.
State the difference between distance and displacement
Distance is a scalar - doesn’t involve direction
Displacement is a vector and is measured in a straight line from the start point to the finish point and the direction of that straight line.
State the difference between speed and velocity
Speed is a scalar
Velocity is a vector
State the following typical speeds: walking Running Cycling Sound
walking - 1.5 m/s
Running - 3.0 m/s
Cycling - 6.0 m/s
Sound - 330 m/s
State the equation with all units to calculate speed
distance (m) = speed (m/s) × time (s)
how can speed be calculated from a distance - time graph
Using the gradient
State the equation to calculate average acceleration, with all units
acceleration = change in velocity / time
acceleration - m/s2
velocity - m/s
time - s
How can acceleration be found from a velocity - time graph
From the gradient
How can displacement be found from a velocity - time graph
From the area under the line
What is the rate of acceleration for an object falling close to the earths surface?
9.8 m/s2
What is terminal velocity and when does it occur?
the maximum velocity an object can fall at, this happens when forces are balanced
What factors can increase the size of air resistance
Speed
Surface area
Density of the fluid which the object is falling through
State Newtons first law
if the resultant force acting on an object is zero the object will stay at rest or move at a constant velocity
The tendency of objects to continue in their state of rest or of uniform motion is called?
Inertia
State Newtons second law
The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.
State the equation with all units for Newtons Second law
resultant force (N) = mass (kg) × acceleration (m/s2)
Define inertial mass
Inertial mass is a measure of how difficult it is to change the velocity of an object
inertial mass is defined as the ratio of force over acceleration.
State Newton’s third law
Whenever two objects interact, the forces they exert on each other are equal and opposite.
Define stopping distance
The stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance).
Define thinking distance
the distance the car travels whilst a driver reacts to a situation
Define braking distance
the distance the car travels whilst the brakes are applied
State the typical reaction times for a human
0.2 s to 0.9 s.
State some factors that can affect a persons reaction times
tiredness, ages, drugs and alcohol, Distractions
State some factors that can affect the braking distance of a car
Rain, ice, snow, poor quality brakes, poor quality tyres, gradient of the road, mass of the car
State the one factor that can increase both the thinking distance and braking distance
Speed
State the equation for momentum
momentum = mass × velocity
State the units for momentum
kg m/s
Define the conservation of momentum
In a closed system, the total momentum before an event is equal to the total momentum after the event.
