Forces Flashcards
Vector quantity
Have magnitude and direction (force, velocity, displacement, momentum…)
Scalar quantities
Only magnitude (speed, distance, mass, temp)
Interaction pair
A pair of forces that are equal and opposite and act on two interacting objects (based on Newtons third law)
Gravitational force is…
Force of attraction between masses
Mass is different to weight how 🤷
Mass is the amount of stuff if an object where as weight is the force due to gravity depending on strength of its field and location.
Uniform object
One with the same density throughout the regular shape
For earth what is the gravitational field
9.8 N/kg
Gravity of moon
1.6 N/kg
Weight and mass are directly proportional ?
👏👏👏👏👏👌
If a resultant force moves an object what is happening
Work is done!
When work is done what happens
Energy is transferred from one store to another as the object moves
One joule of work is done when a…
Force of one newton causes an object to move a distsance of one meter
1J = 1Nm
How do you use scale drawings to find resultant forces
Draw a straight line from the start of the first force to the end of the last force for the resultant force. Measure the length of the resultant force to find the magnitude and the angle to find the direction of the force.
What does equilibrium mean
When forces are balanced and the resultant force = 0
How do you find the missing force acting on an object if it is equilibrium
Draw out the forces you do know, join the end of the last force to the start of the first force. This line is your missing forcd so you can measure the size and direction
Splitting a force into components
Forces at awkward angles can be split into components at right sngles to each other. Acting together the have the same effect aa a single force so toy can resolve a force by drawing a force to scale, and then add the horizontal and vertical components along grid lines. You can then measure them.
Elastic objects
Objects that can be elastically deformed
If an object is ellasticslly deformed then what happens to its energy
All the energy is transfered to the object’s elastic potentail energy store
Extention of a spring is directly proportional to
The load or force applied
Spring constant depends on what
The material that you are stretching
Limit of proportionality of eleasticity
When the extention is no longer proportional to the force
Turning effect of a force
Moment
How to get maximum moment
Need to push at right angles
Levers increase what
The distance from the pivot at which the force is applied
What can different sized forces cause
Change in moment of a force
What are fluids
Substance that can flow as particles aee able to move around and collide with other partilces
Pressure is what
Fore per unit area, meaning particles exert a pressure. It depends on depth and density
What does density measure in a liquid
The compactness of a substance which is uniform in a liquid and doesn’t vary in shape or size
As depth increases what else increases
The number of particles above a point increases (the weight of the particles adds pressure)
What is upthrust
The pressure of a fluid exerting force in every direction
What is upthrust equal to
The weight of fluid that has been displaced by the object
How does an object float
If its upthrust is equal to its weight depending on density
Atmospheric pressure decreases with height as
It is a layer of air that is thin compared to the size of the earth. It is created on a surface by air molecules colliding with the surface. As the altitude increases the air is less dense (fewer air molecules collide with the surface). Also, there are fewer air molecules above a surface as the height increases.
A person walking A person running A person cycling A car A train A plain
1.5m/s 3m/s 6m/s 25m/s 30m/s 250m/s
Uniform acceleration
Just something speeding up at a constant rate
On a distance time graph what is the gradient
Speed (distance/time)
On a distance time graph what is acceleration
The gradient of the tangent to thw curve at that point
On a velocity time graph what is gradient
Acceleration
On a velocity time graph what is the distance travelled
Area under any section of the graph in that time interval
Terminal velocity
Maximum speed where it is a steady speed compared by drag in comparison to weight and frictional force.
Frictional force depends on
Shape and area
Newton’s First Law
If the resultant force on a stationary object is zero, the object will remain stationary. If the resultant force on a moving object is zero, it’ll just carry on moving at the same velocity
Acceleration is proportional to…
The resultant force
Acceleration is inversly proportional to…
Mass
Newton’s second law
Resultsnt force = mass x acceleration
Inertia has the tendecy to do what?
Tendency for motion to remain unchanged, objects at a steady speed will stay moving at that speed (newton’s first law)
Inertia mass can be found using
Newtons second law (F=ma)
Newton’s Third Law
When two objects interact, the forces (same forces) they exert on eachother are equal and opposite
Normal contact force
An object or person giving equal but opposite force back
Stopping distance =
Thinking distance + Braking distance
Thinking distance is effected by:
Speed
Reaction time
Breaking distsnce is effected by
Speed-the faster the vehcile travles, the longer it takes to stop
Weather and road surface-can cause less grip (less friction)
Condition of tires-if tires are bald they can’t get rid of water (skidding)
How good the breaks are-worn breaks won’t apply as much force
Reaction distance effected by
Tiredness
Drugs
Alcohol
Thinking distance increases at the same rate as
Speed
Work done to stop a car is equal to
The car’s kinetic energy store’s energy
As speed doubles in breaking distance the kinetic energy increases how much
4 fold (2 squared) meanind work done increases 4 fold too
Momentum=
Mass x velocity
The greater the mass of an object, or the greater the velocity…
The more momentum the pbject has
Conservation of momentum
The total momentum before an event is the same as after the event
What happens in momentum when a ball with the smas mass a another ball collide
The stationary ball has zero momentum. The moving ball has a veloxity so it has momentum. As the moving ball hits the other, it causes it to move (has momentum). The moving ball countinues to move but at a smaller velocity/momentum as the other ball now has combined momentum to equal the original momentum
If a moving car hits a parked car, what happens to its momentum
The crash causes the cars to lock together, and continue moving in the direction of the original moving car but at lower velocity. Beofre the momentum was equal to the mass of the moving car x its velocity but now the mass of the moving object has increased, but its momentum is equal to before. Sk an increase in mass casues a decrease in velocity
How does resultant force change momentum
Resultant force acting on a moving object changes the velocity, meaning it changes the momentum too.
Force causing change is equal to the rate of momentum
Saftey features of cars:
Crumple zones-increasing time takien for car to stop
Seat belts-increasing time taking for person to stop
Airbags
