Flashcards in 2nd half Forces and Motions Deck (36):
What is the SI unit for mass?
What is the SI unit for distance?
What is the SI unit for speed?
What is the SI unit for acceleration?
What is the SI unit for force?
What is the SI unit for time?
What is the SI unit for gravitational force constant?
What is the SI unit for spring constant?
What is newtons 2nd law?
zero resultant force means an object is either stationary or remains at a constant velocity, if there is a resultant force then the object accelerates.
What is the difference between weight and mass?
Mass is how much matter you are made of and doesn't change whereas weight is a force that acts upon mass.
state the equation that uses weight, mass and gravitational force constant.
weight = mass x gravitational force constant
What is the gravitational force constant on earth?
On Earth when there is no drag how do things fall towards earth?
The acceleration of freefall which is 10m/s2
What act to oppose the direction of motion?
Friction and drag
Drag ________ as velocity ____________.
Drag ___________ as surface area (perpendicular to velocity) ___________
State the equation that uses force, mass and acceleration.
Force = mass x acceleration
Where f is the resultant force
Describe in terms of individual forces and resultant force why falling objects reach terminal velocity.
Object falls because weight is pulling it down
Tiny bit of drag but resultant force downward
Because there is a resultant force it accelerates
As it accelerates drag increases until it is equal and the resultant force is zero
Zero resultant force means no acceleration but constant velocity
Describe an experiment to investigate the force on falling objects
Measure time taken for empty cupcake case to fall from window
Need timer and scale
Drop case and measure time it takes to drop
Work out velocity
To improve drop from higher place or make sure no wind
How do you calculate the linear momentum of an object from its mass and velocity?
Momentum = mass x velocity
How do you calculate the change in momentum for an object that changes velocity?
Work out the initial and final momentum and find the difference.
What is the equation for the principle of the conservation of momentum to objects that collide in order to calculate final mass, velocity or momentum?
Final momentum = initial momentum
for sticky collisions, springy collisions and explosions
What is the equation that states the force is the equal to the change of momentum?
Force = change in momentum/time taken
= final momentum - initial momentum/time taken
Using the equation that states the force is equal to the rate of change in momentum explain how safety features like crumple zones, airbags and seat belts save lives.
force = rate of change in momentum
For same velocity momentum change is the same, crumple zones increase the time of collision
force = change in momentum
This reduces force
State and describe the meaning of the equation that uses stopping distance, thinking distance and braking distance
Stopping distance = thinking distance + braking distance
If a rabbit jumped out on road, you process the thought of braking and you travel a distance while doing so = thinking distance
You press the break and the car takes time to slow down = braking distance
These add up to the overall stopping distance
Describe factors that affect thinking distance, braking distance or both
Thinking - Poor visibility, drunk
Braking - Bad road conditions
Where does the weight of a body act?
Through its centre of gravity
State the formula for a moment
force of moment = force x distance from pivot
State the principal of moments
For an object at equilibrium, the sum if the clockwise moments are equal to the sum of the anticlockwise moments
Explain how forces act on a beam supported at either end on a pivot
They vary with the placement of the load by applying the principle of moments to each of the pivots
Describe an experiment to investigate how extension varies for springs, wires and rubber bands
Hang a spring from a clamp and add weight of 100g measuring the distance each time from the top of the spring to the top of the masses
State Hooke's Law
Extension is proportional to the force applied
k= spring constant
Hooke's law only applies to what?
The linear region of the graph, where force is directly proportional to extension
What is it called when a spring can stretch no more?
The elastic limit or the limit of proportionality
Describe elastic behaviour.
The ability of a material to recover its original shape after the force has been removed.