Forces Flashcards
Scalar quantities
Only have magnitude, no direction
E.g. distance, time, power, mass, energy, current, voltage, charge, frequency
Vector quantities
Has magnitude and direction
E.g. force, acceleration, momentum, velocity
Contact forces
The objects are physically touching
E.g. friction, air resistance
Non-contact forces
The objects are physically separated
E.g. gravitational force, electrostatic force
Weight
The force acting on an object due to gravity
Weight formula
Weight = mass x gravitational field strength
W = m x g
Resultant forces
The sum of all forces acting upon an object
Equilibrium
When there is no resultant force, therefore forces are balanced
Displacement
How far away you are from the original position
Work done formula
Work done - force x distance
W = f x d
Force formula
Force = spring constant x extension
F = k x e
How forces affect the extension of a spring practical
Secure a clamp stand to the bench using a G-clamp
Use bosses to attach two clamps to the clamp stand
Attach the spring to the top clamp, and a ruler to the bottom clamp
Adjust the ruler so that it is vertical, and with its zero level with the top of the spring
Measure and record the unloaded length of the spring
Hang a 100 g mass from the spring and measure the new length of the spring
Turning force / moment formula
Force x perpendicular distance
Levers
They are force multipliers, they create moments
Gears
Allow motion to be transferred from one point to another
They can also increase or decrease the turning force (moment)
Pressure formula
Force / area
Pressure in a fluid
The pressure in fluids causes a force normal (at right angles) to any surface
Pressure in a column formula
Pressure = height of the column x density x gravitational field strength
Upthrust
An object that is submerged experiences a greater pressure on its bottom surface than on its top surface
This causes a resultant force upwards
Factors affecting floating and sinking
Densities of the object
Densities of the liquid
Force exerted by the object
Atmospheric pressure
Air molecules colliding with a surface create atmospheric pressure
The number of air molecules above a surface decreases as the height of the surface above ground level increases
So as height increases there is always less air above a surface than there is at a lower height
So atmospheric pressure decreases with an increase in height
Speed
How fast you are going disregarding direction
Speed formula
Speed = distance / time
S = d / t
Walking, running and cycling speed
Walking - 1.5 m/s
Running - 3 m/s
Cycling - 6 m/s
Speed of sound in air
330 m/s
Velocity
The speed of an object in a particular direction
Acceleration
Amount that velocity changes per unit time
Gradient of the line
Acceleration formula
Change in velocity / time taken
ΔV / t
Acceleration formula (2)
(final velocity)² - (initial velocity)² = 2 x acceleration x distance
Distance travelled on graph
The area under the line
Newtons 1st law
Objects with balanced forces acting on them will stay at rest, or in constant motion
Newton’s Second Law
Force = mass x acceleration
Practical 7
Newtons 3rd law
Every action has an equal and opposite reaction
Stopping distance
Thinking distance + braking distance
Factors affecting braking distance
Wet or icy roads
Condition of the brakes
Speed of the car
Mass of the car
Factors affecting thinking distance
Tiredness
Drugs
Alcohol
Momentum
Product of mass and velocity
Momentum formula
Mass x velocity
M x v
Conservation of momentum
Total momentum before an event = total momentum after an event
E.g. when a gun recoils backwards
Change in momentum formula
Change in momentum = force x change in time
Safety features in a car
Airbags, crumple zones, seat belts
The force of the collision is equal to the rate of change of momentum
These different safety features decrease the rate of change of momentum, which decreases the force of the collision on any people within the car
