P10: Forces And Motion Flashcards
How is resultantforce calculate?
F(N)= Mass x Acceleration
What does Newton’s second law state?
The acceleration of an object is:
● directly proportional to the resultant force on an object
● inversely proportional to the mass of an object
What is inertia?
The tendency for an object to stay at rest or to continue in uniform motion (constant velocity) is called inertia.
What is the inertial mass?
Inertial mass refers to the measure of difficulty in changing an object velocity
m= F/a
An object with more mass has a greater tendency to resist a change in its moving state. More force is required to move a greater mass from rest.
What is the difference between mass and weight?
The weight of an object is the force acting on it due to gravity. Weight is measured in newtons, N.
The mass of an object depends on the quantity of matter in it. Mass is measured in kilograms, kg.
How is weight calculated?
Weight = Mass x Gravitational force (approx 10m/s^2)
What is terminal velocity?
The maximum speed of an object, reached when the forces moving the object are balanced by its frictional forces/ air resistance/ upthrust (liquid)
What occurs as a skydiver opens a parachute?
When the diver opens his parachute the air resistance suddenly increasing, causing him to start slow down.Because he is slowing down his air resistance will decrease again until it balances his weight The skydiver has now reached a new, lower terminal velocity.
What is thinking distance?
The thinking distance is the distance travelled in between the driver realising he needs to brake and actually braking.
What factors may affect thinking distance?
Influence (alcohol/ drugs)
Visibility
Age
Speed
What is braking distance?
The braking distance is the distance taken to stop once the brakes are applied.
What factors may affect braking distance?
- Friction
- Condition of brakes
- Condition of tyres
- Conditions of the road
- Mass of vehicle
How is acceleration/ deceleration calculated (braking)
a= (v^2-u^2)/ (2x displacement)
U= Initial velocity
V= Final velocity
How is breaking force calculated?
F= mass x acceleration
How is momentum calculated?
p= mass x velocity
What is momentum?
A property of a moving object which depends on how much mass the object has and how fast it is moving.
What is the conservation of momentum?
In a closed system, momentum before an event is the same as the momentum after the event.
What is meant by a closed system?
A physical system that does not exchange matter or energy with its surroundings
What is the unit for momentum?
kgm/s
What is the equation for the conservation of momentum to find out velocity of another object
m1u1+m2u2= m1v1+m2v2
M= Mass
U= Initial velocity
V= Final Velocity
What is the conservation of mass in explosions/ jumping off something?
(mass A x velocity A) + (mass B x velocity B) = 0
What safety features does a car have?
Crumple zone
Air bags
Seat belts
How does the ‘crumple zone’ of a car reduce impact of a crash?
- Crumple zone- Reduce the impact of a crash as it is designed to absorb mist f the impact as it ‘crumples’. Increases the time taken to change the momentum to reduce the force
How do air bags reduce impact of a crash?
Reduce the direct impact on those within the car through givung a softer and more gradual stop for the head. The larg surface aeea also dustributes the force of the crash
How do seat belts reduce impact of a car crash
Prevent passenger from falling into thr front and prevent thos ein front seat from faling through the windsheild. Seat belt os spread across the chest to distribute the collision force across a greater surface area.
How can the force changing the momentum of an object be calculated?
F = Change in momentum/ time
What is an elastic object?
An elastic object is an object which regains its shape when the forces are deforming it (e.g stretching or squashing) are removed
When an elastic object is deformed the energy which caused it to deform is stored as elastic energy, which is released when the force is removed.
What is compression?
When a force is exerted on an object (a spring for example) it will be compressed (push the spring together).
What is tension on a spring?
As well as compression an object (spring for example) can be in tension, this is when a force pulls on the object (stretching a spring).
What does it mean if something is proportional?
Corresponding in size or amount to something else
How can the force applied to a spring be worked out?
F (N) = spring constant(N/m) x extension(m)
What happens if a spring passes its limit of proportionality?
The material starts to behave in a non-linear way. The material will no longer continue to deform and be able to regain its original shape
What is a line on a graph called when it increases on y and x
Linear
What is the method for investigation force and extension of a spring?
- Set up the apparatus as shown in the diagram, initially without any masses hanging from the spring
- Align the marker to a value on the ruler, record this initial length of the spring
- Add the 100 mass hanger onto the spring
- Record the mass (in kg) and position (in cm) from the ruler now that the spring has extended
- Add another 100 g to the mass hanger
- Record the new mass and position from the ruler now that the spring has extended further
Repeat this process until all masses have been added - The masses are then removed and the entire process repeated again, until it has been carried out a total of three times, and an average length is calculated
What is equipment used for acceleration practical?
- Pulley Wheel
- Retort stand and clamp
- Weights
- Light gate
- Data logger
- Trolley
- Card + Bluetack
- Mass hanger
How is acceleration calculated in the trolley practical?
The display connected to the light gate measures the time it takes for part A of the card to pass through the light beam. Since it knows the width of the card at A, it can calculate the average speed V1 as width of A/time taken.
The process is repeated for part B of the card and the average speed v2 is calculated.
The software also knows the time, t, to get from A to B so it can calculate the acceleration.
What is the method for investigating force and extension?
1) Set up the apparatus as shown in the diagram initially without any masses hanging from the spring
2) Align the marker to a value on the ruler, record this initial length of the spring
3) Add the 100 mass hanger onto the spring
4) Record the mass (in kg) and change in position (in cm) from the ruler now that the spring has extended. Make sure to check whether the spring has not gone past its limit of proportionality otherwise, it has been stretched too far and will stop obeying Hooke’s law
5) Add another 100 g to the mass hanger
6) Record the new mass and position from the ruler now that the spring has extended further
7) Repeat this process until all masses have been added
8) The masses are then removed and the entire process repeated again, until it has been carried out a total of three times, and an average length is calculated
What are systematic and random errors of the trolley practical?
Systematic Errors:
• Experiment 1: ensure any weights removed from the weight hanger are transferred to the toy car or trolley
• This is to ensure the total mass of the system remains constant
Random errors:
• A main cause of error in this experiment is the measurements of time
• Ensure to take repeat readings when timing intervals and calculate an average to keep this error to a minimum
• Start the toy car by releasing it, allowing it to accelerate under the force of the weights attached by the string
• Ensure not to give it a ‘push’
What is the equation for acceleration?
a= f/m
a= change in v/ time
