P2 Flashcards
How is displacement different to distance?
Both are measures of how far something has travelled, but displacement includes direction. eg. 10m north
How is velocity different to speed?
It describes speed AND direction. eg. 30mph due north
What is a scalar quantity?
Quantities which only involve numbers, eg. speed, distance, mass, time
What is a vector quantity?
Quantities which also have a direction, eg. velocity, displacement, force, acceleration
How do you calculate distance travelled with speed and time?
Distance travelled (m) = Speed (m/s) * Time (s)
What is acceleration?
The rate of change of velocity.
How do you calculate acceleration with change in velocity and time?
Change in acceleration (m/s²) = Change in velocity (m/s) ÷ Time (s)
What does it mean if an object has negative acceleration?
It is either slowing down (decelerating), or speeding up in the negative/opposite direction.
What is uniform acceleration?
Constant acceleration
How do you calculate uniform acceleration with final velocity, initial velocity, acceleration and distance?
(final velocity (m/s))² - (initial velocity (m/s))² = 2 * acceleration (m/s²) * Distance (m)
v² - u² = 2 * a * d
What practical can you perform involving a trolley and a ramp to investigate the relation between distance, speed and acceleration?
Set up a ramp with 3 light gates on it, measure the distance between them.
When the trolley reaches the “runway”, it will travel at constant speed.
The time between 1 + 2 can be used for avg speed on the ramp, and the time between 2 + 3 gives the speed on the runway.
The acceleration of the trolley on the ramp can be found with the initial speed, 0, the final speed (speed on the runway) and the time between 1 and 2.
How big should your measuring instrument be?
If possible, longer than than the distance you’re measuring.
What could you use to measure time?
A stopwatch, although it involves human error.
Light gates connected to a computer.
What does the gradient on a distance-time graph show?
Speed of the object.
What does a flat section on a distance-time graph show?
When the object is stationary
What do curves on a distance-time graph show?
Acceleration
What does it mean if the gradient on a distance-time graph is increasing/decreasing?
The speed is increasing/decreasing.
How can you find the gradient of a specific point on a curve?
Draw a tangent to the curve at that point, and find the gradient of the tangent.
What does the gradient on a velocity-time graph show?
Acceleration
What does a flat section on a velocity-time graph show?
Constant/steady velocity
What do upwards/downwards sections on velocity-time graphs show?
Acceleration/decelleration
What does a curve on a velocity-time graph show?
Changing acceleration
What does the area beneath any section of a velocity-time graph show?
The distance travelled in that time interval
What are examples of contact and non-contact forces?
Contact - friction
Non-contact - electrostatic, magnetic, gravitational
What is resultant force?
If a number of forces act a single point, you can replace them with a single force called the resultant force.
What does it mean if an object has a resultant force of 0?
It is either stationary or moving at a constant/steady speed.
What does it mean if an object has a resultant force which isn’t 0?
It will either be accelerating or decelerating because the forces are unbalanced.
How do you draw the forces acting on an object when trying to find the size and direction of a resultant force?
tip-to-tail.
What does it mean if an object is in equilibrium?
It has zero resultant force.
What is Newton’s First Law?
An object will remain stationary or at a constant velocity unless acted on by an external force.
What is Newton’s Second Law?
The force acting on an object is equal to its rate of change of momentum.
How do you find force using mass and acceleration?
Force (N) = Mass (kg) * Acceleration (m/s²)
What is friction?
When an object is moving, friction acts in the direction that opposes movement. It makes things slow down/stop.
What is needed to oppose friction?
A driving force to keep an object moving.
What happens if the driving force is equal to the friction force?
The object will move at a steady speed
What happens if the driving force is greater than the friction force?
The object will accelerate
What happens if the driving force is less than the friction force?
The object will decelerate
What is the difference between friction and drag?
Friction occurs between two surfaces in contact, whereas drag occurs when an object passes through a fluid.
How is resistance related to velocity?
Resistance is directly proportional to velocity - as velocity increases, so does resistance.
What does it mean when an object has reached terminal velocity?
An object reaches terminal velocity when the acceleration is reduced and the friction force is equal to the driving force.
How does drag affect terminal velocity?
The greater the drag (or air resistance/friction) of an object, the lower the terminal velocity.
What is inertia?
Inertia is the measure of how difficult it is to change an object’s velocity.
What is inertia dependent on?
The mass of the object - the larger the mass, the larger the inertia, and the harder it is to change the object’s velocity.
What is Newton’s Third Law?
When two objects interact, the forces they exert on each other are equal and opposite.
How do you calculate Momentum with Mass and Velocity?
Momentum (kg m/s) = Mass (kg) * Velocity (m/s)
How do you calculature Force with Change in Momentum and Time?
Force (N) = Change in momentum (kg m/s) ÷ Time (s)
What is the law of conservation of momentum?
In a collision where no other external forces act, momentum is conserved ie. the total momentum after the collision is the same as it was before it.
What is an elastic collision?
Where the total energy in the KE stores of the objects colliding is the same before and after the collision ie. the energy is conserved.
What is an inelastic collision?
Where some of the energy in the KE stores is transferred to other stores. eg. Energy can be transferred by heating or sound.
What is gravity?
The force of attraction between all masses
How does the size of an object affect its gravitational field?
The bigger an object, the bigger its gravitational fiel dis.
What is g?
Gravitational field strength, also known as the acceleration due to gravity.
What is g on Earth?
10 N/kg (or 10 m/s²).
How do you calculate the weight (gravity force) of an object using mass and g?
Gravity force (N) = Mass (kg) * Gravitational field strength (N/kg)
How is weight affected by gravitational field?
The stronger the gravitational field an object is in, the higher the gravitational field strength and so the larger the object’s weight.
When does an object have energy in its gravitational potential energy store?
When it is at any height above the Earth’s surface.
How do you calculate gravitational potential energy, using mass, height and g?
GPE (J) = Mass (kg) * Height (m) * g (N/kg)
When does an object have energy in its kinetic energy store?
When it is moving. This energy depends on mass and velocity.
How do you calculate Kinetic Energy, using mass and speed?
Kinetic energy (J) = 0.5 * Mass (kg) * (speed)² (m/s)²
When is work done?
When a force makes an object move, energy is transferred and work is done.
How do you calculate Work done, using Force and Distance?
Work done (J) = Force (N) * Distance (m)
What is power?
The rate at which energy is transferred.
How do you calculate the Power of an object, using Work Done and Time?
Power (W) = Work done (J) ÷ Time (s)
What is 1 watt equal to in joules?
1 watt = 1 joule of energy transferred per second
What is deformation?
When you apply force to an object and it is stretched, compressed or bent.
What is elastic deformation?
When an object returns to its original shape after the forces acting on it are removed.
What is plastic deformation?
When an object doesn’t return to its original shape when forces are removed.
What is the relationship between the extension of a spring and the force that the spring exerts?
They were directly proportional.
How do you find the force exerted by a spring, using extension and spring constant?
(Hooke’s law) Force exerted by a spring (N) = Extension (m) * Spring constant (N/m)
Why do objects begin to disobey Hooke’s law at a certain point?
Until a certain point, force and extension have a linear relationship. However, past a certain point, the object stops deforming elastically and begins to deform plastically.
What is the maximum force that can be applied to a material before it begins to deform plastically?
The elastic limit
How can you investigate the extension of a spring?
Hang a spring from a clamp stand, the measure the spring’s length (original length).
Weigh masses and add them one at a time to the spring, so the force increases.
After each mass is added, measure extension.
How is work involved in deforming an object?
When an object is deformed by a force, work is done to stretch, compress or bend the object.
How do you find the energy transferred in stretching, using the spring constant and extension?
Energy transferred in stretching (J) = 0.5 * Spring constant (N/m) * (extension)² (m)²
How do you find the energy transferred during deformation with a graph?
Find the area beneath the curve.
What is a moment?
The turning effect of a force
How do you calculate the moment of a force, using force and distance?
Moment of a force (Nm) = Force (N) * Distance (m)
What is the relationship between total anticlockwise moments and total clockwise moments?
Total anticlockwise moments = total clockwise moments
What do levers do?
They increase the distance from the pivot that the force is applied, so less input force is needed to reach the same moment.
What does “force multiplier” mean?
They reduce the force needed to reach the same moment.
What equation can be written as a result of the relationship between the input force/output force?
Input force ÷ output force = Distance of output force from pivot ÷ Distance of input force from pivot
What are gears?
Circular cogs with “teeth” around their edge.
How do the “teeth” in gears work?
The teeth of different gears interlock so that turning one gear causes another to turn as well. Because of how they are linked, a gear spinning clockwise will make the next spin anticlockwise.
How do gears make moments larger?
A force applied to a small gear creates a small moment. The small gear applies the force to the next gear, which is larger. The force on the larger gear is further from the pivot and so the moment is larger.
How is pressure in a fluid transmitted?
Equally in all directions and it causes a force at right angles to any surface.
How can you find pressure with force and area?
Pressure (Pa) = Force (N) ÷ Area (m²)
What are hydraulic systems?
They are used as force multipliers. They use a small force to produce a bigger force.
How do hydraulics work?
They have 2 pistons, one with a smaller cross-sectional area than the other. Pressure is transmitted equally through a liquid, so the pressure at both pistons is the same.
The smaller piston transmits pressure to the 2nd which experiences the same pressure but has a larger area. Therefore, there is a larger force.
