Forces Flashcards
Give 4 vector quantities.
- Force
- Velocity
- Displacement
- Momentum
Give 4 scalar quantities.
- Speed
- Distance
- Time
- Mass
What is an interaction pair?
A pair of forces that are equal and opposite and act on two interacting objects
What is weight?
The force acting on an object due to gravity
2 factors that increase gravitational field strength?
- getting closer to the mass causing the field
- increasing size of the object
What is a uniform object?
An object which density is the same throughout
What is a centre of mass?
The point at which all mass of an object is concentrated
Give the equation for mass.
Mass = weight x gravitational field strength
What is mass and weight’s relationship?
Directly proportional
Give the equation for amount of work done.
Work = force x distance
What happens when “work is done”
A force moves an object and energy is transferred from one source to another
Which way do you draw the resultant force on a scale drawing?
Tail of the first arrow to head of the last arrow
How to find the direction of a resultant force on a scale drawing?
Measure the angle at the tails to find a bearing
How is equilibrium shown on a scale drawing?
The head of the last force should meet the tail of the first force (no resultant force so arrows all go same way)
What to do with diagonal forces on a scale diagram?
Split them into vertical and horizontal components
What does elastically deformed mean?
An object has been compressed/ stretched but can return to its original shape/ length
What does inelastically deformed mean?
An object has been stretched/ compressed but can’t return to its original shape/ length
Extension equation?
Force = spring constant x extension
Relationship between extension and force applied?
Directly proportional
What is the limit of proportionality for force & extension
When force and extension are no longer directly proportional after a maximum force
Give the equation for a moment.
Moment = force x perpendicular distance from pivot to line of action for force
What happens if an anticlockwise moment = clockwise moment?
The object won’t turn
How do levers make work easier?
By increasing perpendicular distance from line of action by force (less force is needed to achieve same moment)
What are gears used for?
To transmit the rotational effect of a force from one place to another
Equation for pressure at the surface of a liquid?
Pressure = Force normal to that force/ area of surface
How does density differ in a liquid/gas?
In liquid, density is uniform - same everywhere - in a gas it can vary
How does density affect pressure on a liquid?
The denser a liquid, the higher the pressure as there are more particles in a certain volume, so more collisions happen.
How does depth affect a liquid’s pressure?
The deeper in a liquid, the more particles above the point, the weight of these particles adds to the pressure
What are 2 factors that affect a liquid’s density?
- Density
- Depth
Equation for a liquid at a certain depth?
Pressure = height of column of liquid (depth) x gravitational field strength x density of liquid
What is upthrust equal to?
The volume of water which has been displaced by the object
What is upthrust?
The resultant force which pushes an object upwards if it has been submerged
What causes an object to float?
If the upthrust is equal to the object’s weight, so the forces balance
What causes an object to sink?
If the weight is greater than the upthrust
Explain how an object floats in terms of density.
- An object that is less dense than the fluid it is in will weigh less than an equal volume of that liquid. – - It displaces a volume of liquid equal to its weight, so the water displaced is less than the object’s volume
- This means the object sticks out of the water and not fully submerged however the weight is equal to the upthrust so it floats
Explain sinking in terms of density?
An object denser than the fluid it is in will not be able to displace a volume of water equal to its weight, meaning weight is always greater than upthrust.
What is atmospheric pressure?
Particles from the air colliding with a surface
Why does atmospheric pressure decrease with altitude? (2)
- There are fewer air molecules and the air is less dense so collisions become rarer
- Also there are fewer molecules above you, so weight decreases
Equation for speed?
Speed = distance/time
What is velocity?
Speed with a given direction
2 factors which can affect walking speed?
- age
- terrain
What impacts speed of sound?
Medium it travels through
What affects windspeed?
Large buildings
Equation for velocity?
Acceleration = change in velocity/ time
Average speeds for a person walking, running, cycling?
- 1.5 m/s
- 3 m/s
- 6 m/s
Average speed of a bus, train, plane?
- 25 m/s
- 55 m/s
- 250 m/s
Equation for uniform acceleration?
Final velocity^2 - Initial velocity^2 = 2 x acceleration x distance
What does the gradient equal on a distance time graph?
Speed
What does a flat section represent on a distance time graph?
Stationary
What does a straight uphill section mean on a distance time graph?
Constant speed
What does a curve represent on a distance time graph?
Acceleration/ deceleration
What does the gradient represent on a velocity time graph?
Constant acceleration/ deceleration
What does a flat section away from 0 mean on a velocity time graph?
Constant speed
What does a curve mean on a velocity time graph?
Changing acceleration/ deceleration
How to find the distance travelled on a velocity time graph?
Area under the graph
What forces must balance for constant speed?
Driving forces & frictional forces
What is drag?
Friction or resistance from travelling through a fluid
How is drag reduced?
Streamlining so fluid can flow easily across it
What 2 things can increase drag?
.1. Increased speed
2. Large surface area
Explain terminal velocity.
- Weight is greater than air resistance/drag so the object falls quickly
- As speed increases, drag increases until the forces are balanced, reaching terminal velocity
What is Newton’s first law?
If the resultant force on stationary object is zero, it will remain stationary. If the resultant force on a moving object is zero, it will continue moving at constant velocity.
What are the 5 different forms of acceleration?
Starting, stopping, speeding up, slowing down, changing direction
Relationship between acceleration & resultant force?
Directly proportional
Relationship between mass & acceleration?
Inversely proportional
What is Newton’s second law?
Force = mass x acceleration
What is an object’s inertial mass & how is it found?
How difficult it is to change the velocity of an object (found using Newton’s second law)
What is Newton’s third law?
When two objects interact, they produce equal, opposite reactions
What are the 2 components of stopping distance?
Braking distance + thinking distance
2 factors that affect thinking distance?
- Speed
- Reaction time
3 conditions that impact braking distance?
- Speed
- Weather conditions
- Condition of tyres
How does braking work?
When brakes are pressed, brake pads are pressed onto the wheels causing friction until the friction equals the driving force and the car stops
Why can extreme brakes damage the car?
When braking, energy from the kinetic store transfers to the thermal energy store
- If too much energy transfers the brakes could overheat
3 factors which can affect reaction time?
- Drugs
- Alcohol
- Tiredness
Why does thinking distance increase with speed?
Thinking distance stays constant, but the faster the car moves, the more ground travelled by the car in a shorter time
2 factors which can increase momentum?
- Big velocity
- Big mass
Equation for momentum
Momentum = mass x velocity
What is conservation of momentum?
In a closed system, the total momentum before an event will equal the total momentum after
What can change momentum?
A non-zero resultant force changes an object’s velocity, therefore changing momentum
What does F=m x v-u/t mean?
Force is equal to the rate of change of momentum
What are risks of momentum changing majorly very quickly?
Forces on the body will be very large, meaning large impacts
3 safety features on cars?
- Crumple zones to increase time taken for car to stop
- Seat belts stretch slightly to increase time taken for passenger to stop
- Air in air bags slows you down gradually