Topic 5 - Forces Flashcards
(33 cards)
What is the difference between scalar and vector quantities? Give some examples of each.
Scalar:
— Have magnitude only e.g. distance, time, temperature, speed, mass etc.
Vector:
— Have magnitude and direction e.g. displacement, acceleration, force, velocity etc.
What is the definition of a force?
Force:
— A push or pull acting on an object caused by an interaction with another object
What are the two types of forces? Give examples of each.
Contact:
— Friction, air resistance, tension, normal contact force
Non-contact:
— Gravitational force, magnetic force, electrostatic force
What is the definition for mass in comparison to weight?
Mass:
— The ‘amount of stuff’ in an object
Weight:
— The force acting on an object due to gravity. Weight depends on the gravitational field strengthj of where the object is.
NOTE: weight and mass are directly proportional so if one doubles for example then so does the other
How do you calculate weight?
Weight(N) = mass(kg)*gravitational field strength(N/kg)
What is the resultant force?
The resultant force on an object is when you replace all the forces acting on an object with a single force. This single force is known as the resultant force.
How do you work out the work done when a resultant force moves an object?
Work done(J) = Force(N) * distance(m)
What is the difference between elastic and inelastic deformation?
When an object has been elastically deformed, it will return back to its original shape and length once the applied force has been removed whereas with inelastic deformation, once the object has been stretched, bent or compressed, it does not return back to its original shape and length.
What is the equation that links force, spring constant and extension?
Force(N) = spring constant(N/m) * extension(m)
NOTE: extension is directly proportional to force
What does the limit of proportionality indicate and how is it shown on a graph?
Limit of proportionality indicates the extension is no longer directly proportional to the force. This can be shown on an extension-force graph where the graph begins to curve.
How do you calculate the pressure at the surface of a fluid?
Pressure(Pa) = force(N) / area(m^2)
How do you calculate the pressure of a liquid at a certain depth due to the column of liquid?
Pressure(Pa) = height aka depth(m) * density(kg/m^3) * gravitational field strength(N/kg)
What is upthrust?
Upthrust is the resultant force upwards when the force exerted on the bottom of an object is larger than the force exerted from the top. Upthrust is equal to the weight of the object that has been displaced.
What factors influence an object floating and sinking?
An object floats if the weight of the object is equal to the upthrust. It sinks if the object weighs more than upthrust because it is more dense.
How does atmospheric pressure change with changhung altitude?
As altitude increases, atmospheric pressure decreases. This is due to the fact that as altitude increases, the atmosphere gets less dense.
What are some typical values of speed?
Walking - 1.5 m/s Running - 3 m/s Cycling - 6 m/s Car - 25 m/s Train - 55 m/s Plane - 250 m/s Sound in air - 330 m/s
What is the equation that links speed, distance and time?
distance travelled(m) = speed(m/s) * time(s)
How do you calculate the speed of an object on a distance-time graph when the object is:
- – moving at a constant speed in a straight line?
- – changing speed?
— Work out speed by finding gradient of the straight line on the graph where it is moving at a constant speed.
— Draw a tangent at a particular point on the curve and work out the gradient of the tangent
How do you work out acceleration and distance travelled on a velocity-time graph?
Acceleration:
— Finding gradient of the graph
Distance travelled:
— Finding the area under the graph
What is the equation for acceleration and uniform acceleration (constant acceleration)?
Acceleration:
— acceleration(m/s^2) = change in velocity(m/s) / time(s)
Uniform acceleration:
— (final velocity)^2 - (initial velocity)^2 = 2accelerationdistance
What is terminal velocity? Link terminal velocity to the idea of a parachute.
Terminal velocity:
— The maximum speed an object reaches when falling.
—With a parachutist, when the parachute is first opened the force of weight is larger than air resistance which causes the parachutist to accelerate. As speed increases, air resistance builds up and eventually the force of air resistance is equal to the force of weight. This causes the parachutist to fall at a steady speed meaning it has reached its terminal velocity.
What is Newton’s first law of motion?
Newtons first law:
— If the resultant force on a stationary object is zero then it will remain stationary and if the resultant force on a moving object is zero, then it will continue to move at a constant speed in the same direction therefore the velocity of the object will remain the same.
What is inertia? Also, what is inertial mass?
Inertia:
— The tendency of objects to continue in their state of rest or uniform motion.
In other words:
— The resistance of objects to change their motion.
Inertial mass:
— A measure of how difficult it is to change an object’s velocity.
What is Newton’s second law of motion and the equation linked to this?
Newton’s second law:
— The resultant force on an object is directly proportional to the acceleration of an object and the acceleration of an object is inversely proportional to the mass of an object.
Equation: Resultant force(N) = mass(kg) * acceleration(m/s^2)
