P2: Forces Flashcards
What are scalars?
Quantities with only magnitude.
What are vectors?
Quantities with magnitude AND direction.
Give some examples of contact forces.
Friction, air resistance, tension.
Give examples of non-contact forces.
Electrostatic, magnetic, gravitational.
If an object has zero resultant force, what is it doing?
Either travelling at a constant speed or not moving.
What is a resultant force?
The overall effect of several forces added together.
What is it called when all of the forces acting on an object are balanced?
Equilibrium.
Where is the centre of mass on an object?
Where all of the lines of symmetry cross.
What is the difference between mass and weight?
Mass is the quantity of matter in an object, weight is a force acting on an object. Weight depends on the strength of the gravitational field, mass does not.
What is the moment of a force?
The turning effect of the force.
How do you calculate the moment of a force?
Moment = Force x Distance
What does a lever do?
Increases the turning effect without you needing to use more force.
What are gears used for?
Transmitting the rotational effects of forces. Apply the same force, but with different moments.
Describe the gear movement for a bike on a low gear.
The small gear turns the large gear. Same speed but lower moment.
Describe the gear movement for a bike on a high gear.
Large gear turning the small gear. Same speed but a higher moment.
What states of matter are fluids?
Liquids and gases.
Describe the movement of particles in fluids.
Can move around freely.
Describe the movement of particles in solids.
Can only vibrate around a fixed position.
What happens when an object is placed in a fluid?
The fluid’s particles constantly collide with it.
Describe how the density of the atmosphere changes at different altitudes.
The higher the altitude, the less dense the atmosphere, so the lower the atmospheric pressure (because the number of air molecules decreases).
Describe how pressure changes as depth changes in a fluid.
Pressure increases with depth because of the weight of the liquid above.
List the three things that pressure in a liquid is affected by.
Height, density, gravitational field strength.
What is the equation for pressure in a liquid?
Pressure = height x density x gravitational field strength
What is displacement?
How far an object moves measured from start to finish in a straight line. The overall change in the position of an object
What is the difference between velocity and speed?
Velocity is a vector quantity (has direction), speed is a scalar quantity
What does uniform acceleration mean?
The amount of acceleration doesn’t change.
What is Newton’s first law?
States the movement of an object with 0 resultant force will remain constant.
What is Newton’s Second Law?
States that resultant force = mass x acceleration
What is Newton’s Third Law?
When two objects interact, they exert an equal and opposite force on eachother.
What is inertia?
The tendency of objects with mass to stay at rest or in the same state of motion.
How do you calculate inertial mass?
mass = force/area
What is the equation for stopping distance of a vehicle?
Stopping distance of a vehicle = thinking distance + braking distance.
What factors affect thinking distance?
Tiredness, use of drugs.
What is thinking distance?
How far the vehicle travels during the driver’s reaction time.
What is braking distance?
The distance travelled once the brakes have been applied.
What is braking distance affected by?
Poor condition of the vehicle, weather conditions, wet or icy roads and poor road surfaces.
State the equation that links braking distance and velocity.
Braking distance = k x velocity^2
What do brakes use to slow down wheels?
Friction.
Describe how brakes work.
The work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle.
What are the two things that acceleration depends on?
Force and mass.
What equipment do you need to test how changing the force applied to a trolley changes its acceleration?
Trolley, pulley, slotted masses, two light gates, track
How do you reduce the effect of friction when calculating acceleration in an RPA?
Use an air track, or make a slope
Explain why the temperature of brakes increases as they are used.
-Work is done due to friction
-Causing an increase in the thermal energy of the breaks
What is a closed system?
A system where the total energy remains constant.
How could a driver of a car increase the moment about the pivot of the handbrake lever
Make the driver place their hand at the end of the lever
The driver of a car is distracted, and needs to apply the breaks suddenly to stop the car. Explain why the distraction will increase the stopping distance.
-Stopping distance includes thinking distance
-There is an additional time before the driver applies the brakes
-So the thinking distance will increase
How does having a flexible layer of protection reduce the damage done on collision?
-Increases time taken for the collision to occur
-So the rate of change of momentum decreases
-So the force is reduced
What type of deformation is it if the deformation is reversed when the force is removed?
Elastic.
What is the opposite of elastic deformation?
Inelastic deformation.
What type of deformation is it, if it is not fully reversed when the force is removed?
Inelastic deformation.
What is the elastic limit?
The furthest point a material can be stretched or deformed while being able to return to its previous shape.
The higher the spring constant, the ___ the string?
Stiffer.
What is the equation of Hooke’s law?
Force = Spring constant x extension
When testing how forces affect the extension of a spring, what should be done to avoid equipment falling off the table?
Use a G-clamp to secure the stand.
When testing how forces affect the extension of a spring, what should be done to avoid the sharp end of the spring recoiling if the spring breaks?
Support and gently lower masses whilst loading the spring, and wear eye protection.
When testing how forces affect the extension of a spring, what should be done to avoid masses falling to the floor if the spring fails?
Gently lowering the load onto the spring and taking a step back.
What is momentum?
The product of mass and velocity.
What is Hooke’s law?
The extension of a spring is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.
