Forces GCSE Flashcards
Scalar Quantities
Quantities with magnitude only
Vector Quantities
Quantities with magnitude and direction
Can be represented with an arrow
Force
A push or a pull acting on an object due to the interaction with another object
Types of forces
Contact and non-contact
Examples of contact forces
- Friction
- Air resistance
- Tension
- Normal contact force
Examples of non-contact forces
- Gravity
- Magnetic force
- Electrostatic force
Examples of scalar quantities
- Mass
- Time
- Distance
- Speed
Examples of vector quantites
- Velocity
- Weight
- Force
- Displacement
Weight Formula
W = MG
Weight = Mass x Gravitational field strength
What is the relationship between weight and mass?
Directly proportional
How is weight measured?
Newton meter
Resultant force
The single force which has the same effect as all of the forces acting on it
Work done
When a force causes an object to move through a distance
Work done formula
WD = FD
Work done = Force x Distance
Elastic deformation
If an elastic object is stretched, bent or compressed, it returns to its original shape once the forces are removed
Inelastic deformation
When an object does not return to its original form after being bent, compressed or stretched
Hooke’s Law
F = ke
Extension of an elastic object is directly proportional to the force applied to it, providing the limit of proportionality is not exceeded
Elastic potential energy formula
Ep = 1/2ke^2
What is a moment
The turning effect of a force
Moment formula
M = FD Moment = Force x Distance
What happens when an object is balanced?
The total clockwise movement about a pivot is equal to the total anticlockwise movement
What do levers and gears do?
Act as a force multiplier by the use of moments.
Make moving heavy objects easier because less effort can be put in but for a greater force output
What is a fluid (pressure?
Liquid or gas
How does pressure exert forces in a fluid?
Pressure exerts force at right angles to any surface
Pressure formula (1)
P = F / A
Pressure formula (2)
P = hpg
Pressure = Height of column x density of water x gravitational field strength
Pascals, meters, kg/m^3, N/kg
What is upthrust?
The resultant force upwards due to greater pressures on the bottom an object
Displacement
The distance an object moves in a straight live from the start point to the end point
Speed of sound in air
330 m/s
Distance formula
Distance = Speed / Time
Velocity
Speed associated with a given direction.
Distance/Time Graph
Used if an object moves along a straight line.
Gradient of a Distance/Time Graph at time t.
Speed at time t.
Acceleration
The rate at which speed changes over time
Formula for acceleration
(v-u)/t - Change in Velocity over time
Gradient of a Velocity/Time Graph at time t.
Acceleration at time t
Area under a Velocity/Time graph represents…
The displacement of the object.
Equation for uniform acceleration
v^2-u^2=2as
Newtons first law
If a body is at rest or moving at constant speed in a straight line, it will remain at rest or in motion at constant speed until acting upon by a force
Inertia
The tendency of an object to continue in their state of rest or uniform motion
Newtons second law
F = ma
Force directly proportional to the acceleration of an object
Inertial mass
A measure of how difficult it is to change the velocity of an object
Newtons third law
Whenever 2 objects interact, they exert equal and opposite forces on each other. The two forces must act on the two different objects and the force must be of the same type
Stopping distance
Distance an object travels, calculated by the sum of the braking distance and the thinking
The greater the speed, the greater the stopping distance
What factors can influence reaction time
- Tiredness
- Drugs
- Alcohol
- Distractions
What methods are used to measure reaction time?
- Ruler drop test
Factors affecting braking distance
- Rain
- Ice
-
Factors affecting braking distance
- Rain
- Ice
- The greater the speed, the greater the braking distance because more braking force is required
- The greater the braking force, the greater the deceleration of the vehicle so the stopping distance is decreased
What affects braking distance (forces)
When a force is applied to the brakes of a vehicle, work is done by the friction force between the brakes and the ground, so the wheel reduced kinetic energy of the vehicle and the temperature of the brakes increases
What are the dangers of large decelerations
- Tires may overheat due to friction between the tyre and the road
- Causing it to wear out
- So less grip for rainy or icy conditions
- Which could cause future accidents
- Loss of control, skidding
Momentum formula
P = MV
What is the total momentum change after a collision between two or more objects in a closed system?
No change - total momentum after an event is equal to the total momentum before an event
When does a change in momentum occur?
When a force acts on an object that is moving
What is an equation for momentum involving force?
F = mΔv / t
What are some safety features to reduce momentum of impact?
- Seatbelts
- Air bags
- Cushioned playground surfaces
- Cycle helmets
- Crash mats
How do safety features reduce the momentum of an impact?
- Increases time taken for impact to stop during a collision
- So stopping time increases
- Which decreases acceleration
- So force decreases (f = ma)
- So rate of change of momentum decreases
