P10 (Force And Motion) Flashcards
2 effects of gravity
- on planet surfaces it makes things fall
- gives everything a weight
Mass
This is the amount of things inside an object
Weight
- This is the force acting on an object due to gravity caused by the gravitational field
- can change depending on the strength of the gravitational field
Centre of mass
The force acting from a single point, at the centre
Weight (N)
Mass (kg) x gravitational field strength (N/Kg)
If an object is equilibrium
If all the force acting on the object give a resultant force of 0
3 ways energy transfers through forces
- stretching
- compressing
- bending
What makes something ‘elastic’?
- If an object is elastically deformed it can go back to the original shape once the force is removed
- all energy is transferred to the elastic energy store
What makes an object “inelastic”?
- does’t return to original shape after force is removed
- not all energy is transferred to elastic potential energy
Force, Spring constant, Extension equation
Force(N) = SC(N/m) x Ext(m)
Friction
- makes things stop if there is no force
- acts in opposite direction
- between 2 objects
Drag
- resistance you get in either a gas or liquid
- keeping objects streamlined reduces drag as the fluid can flow easily across it
Terminal velocity
- free falling objects accelerates as gravity stronger than frictional force
- eventually friction builds up and the two forces will be equal where it reaches a terminal velocity (constant speed)
2 factors terminal velocity depend on
- shape
- area
Newtons 1st law
- if the resultant force of a stationary object is 0, it will stay stationary
- if the resultant force of a moving object is 0, it will carry on moving at the same velocity
Newton’s 2nd law
- larger resultant force, quicker the acceleration as they’re directly proportional
- large mass, accelerate less than a smaller mass at a constant resultant force
Resultant force (N)
Acceleration(m/s^2) x Mass(Kg)
Inetia
tendency for a motion to remain unchanged in objects at rest or moving (Newton’s 1st law)
Inertia Mass
- how difficult it is to change the velocity of an object
- done by Force / acceleration finding the ratio
Newtons 3rd Law
When two objects interact the forces exerted on each other are equal and opposite
4 Stages of Newton’s second law practicle
1) Connect trolley to piece of string with the mass
2) Make a start line for the trolley to the light gate
3) release the pulley and measure the acceleration of the system from the light gate
4) repeat the experiment to find an average acceleration
Stopping Distance =
Thinking distance + breaking distance
2 factors your thinking distance is effected by
- speed
- reaction time
4 things your braking distance is effected by
- speed
- weather/ road surface in ice conditions less friction
- condition of the tires
- quality of the breakes
How do brakes work?
- brake pads pushed against wheels
- causes friction and work to be done
- kinetic to thermal energy
- higher speeds= higher breaking force but can be dangerous
What is reaction time + 4 factors affecting it?
- time taken between a stimulus and your reaction in response
- tiredness, drugs, alcohol and distractions
Why does speed effect braking distance more than thinking distance?
- thinking distance is linear and constant to the speed
- more work is done, as speed doubles the kinetic energy increases 4 fold (2^2)
Momentum(kg m/s) =
Mass(kg) x velocity(m/s)
Conservation of momentum
In a closed system the total momentum before the event is the same after the event
Explain how momentum is passed
- with a stationary pool ball the momentum is 0
- as the moving pool ball collides with the stationary the momentum passed on is equal to the original momentum
- the pool ball looses momentum drastically
Force (N) =
- for momentum
Change momentum(kg m/s) / change time(s)
3 car safety features
- crumple zones increase time for car to stop
- seat belts stretching increase time for person to stop moving
- air bags inflate to increase the time to stop by the compressed air
