Flashcards in Forces Deck (27):
What happens when you apply force to an object?
It may stretch or change shape
What is an elastic object?
Any object that can go back to its original shape after the force has been removed
What happens when an object changes shape?
Work is done to the object and the energy is stored by the object as elastic potential energy
What happens to elastic potential energy?
It is converted to kinetic energy when the force is removed and the object returns to its original shape, eg a spring or elastic band bouncing back
What is the equation and how does extension of elastic object work?
The extension is directly proportional to the force or load
Extension = metres
Force = Newtons
F=k x e
K is the spring constant - measured in Newtons per minute (N/m)
When does this stop working?
There is a limit to the amount of force you can apply to an object to keep extension proportional
For small forces and extension are proportional
The limit of proportionality is the maximum force that the object can take and still extend proportionally
Some examples of elastic potential?
Scrunchies for hair
What is the effect of balanced forces and unbalanced forces?
Balanced forces produce NO change in movement
Unbalanced forced change the speed and/or direction of objects
What is a resultant force?
In most situations there are at least 2 forces acting on an object
The overall effect decides the motion of the object
If several forces acting then replace them with a single force which is the same as all the original forces acting together
This is the winning force between forces being applied to an object
It must have a direction
If original forces act along same line then overall effect found by adding or subtracting them
What are the forces on a moving motorcycle or similar object?
Upthrust of the earth - contact force
Driving force - force of engine
Gravity or weight
If the gravity is 9.8 and the mass of the bike and cyclist is 560 then what is the weight?
Gravity x mass = weight
9.8 x 560 = 5488N
To make the bike accelerate what force is increased?
As velocity increases what other force increases?
Air resistance increases and balances the driving when the acceleration stops
This creates a higher constant velocity
What happens to a moving object when the forces on it change?
A moving object will remain moving at a constant speed in a straight line unless upon by an external and unbalanced force.
If a plane is traveling at steady velocity and the engine thrust is 8000N then what is the air resistance?
If the mass of the aircraft and pilot is 670kg what is the force of uplift provided by the wings?
670 kg uplift
If the pilot turns off the engine and the plane starts to fall then what force increases as it falls?
Gravity or weight
What is terminal velocity?
Downward force of gravity equals the upward force of air resistance so the object neither accelerates nor decelerates
What is mass?
What is weight?
How do you calculate weight?
Mass is a measure of the amount of material an object is made of. Measured in kgs.
Weight is the force of gravity on an object. Measured in Newtons (N)
Weight = mass x gravitational force field
N = kg x N/kg
Name types of forces?
Forces have a size and direction - vector quantities
Force = push, pull, twist
Change = shape, direction, speed
Contact force = forces that touch or make contact
Non contact force= act at a distance eg magnets
Force meter = Newton meter
What is friction?
Friction resists the movement of an object
Measured in Newtons (N)
Examples of friction
Friction is useful for:
Lighting a match
Friction is unwanted for:
What is falling?
An object falls through air
Accelerates due to gravity
Air resistance increases
Gravity and air resistance balance when equal
Object stops accelerating and moves at constant speed
This is terminal velocity
How do we calculate speed and what is the difference between speed and velocity?
Speed (velocity) = distance/time - measured in metres per second
Speed is how fast you are going with no regard to direction- 30 mph
Velocity is speed and with direction specified - 30 mph north
How do we calculate distance?
Distance = velocity x time
Measured in metres
How do distance time graphs look and important notes?
Gradient = speed
Stationary or stopped = flat line
Constant speed = straight upward diagonal line - steeper is faster
Increasing speed = line curving upwards - increasing gradient
Decreasing speed = line curving up & levelling off - decreasing gradient
Downhill = going back towards starting point