Forces Flashcards
Contact and Non- contact forces
Give the definition and examples
A contact force is any force that requires contact to occur. Examples include reaction forces (e.g. an object at rest on a surface), tension force (e.g. an object that is being stretched), friction (e.g. two objects sliding past each other), air resistance (e.g. an object moving through the air).
Non - contact forces are forces that don’t need contact to occur. For example, a magnetic force, electrostatic force, gravitational force.
Understand how vector quantities differ from scalar quantities
Understand that force is a vector quantity.
Weight
A scalar quantity has only a magnitude. For example, speed
A vector quantity has both magnitude and direction. For example, velocity.
Force is a velocity quantity and we measure it in Newton.
Weight is also measured in Newton.
Newton’s Third Law
Definition - for every action there is an equal and opposite reaction.
We call the first force the action and the second force the reaction. This means that the reaction force happens AFTER the action force. For example, when you sit down, your weight will pull you down which is the action force but the force acting upwards is the reaction force.
Accelerate meaning
Getting faster, changing direction or changing speed, CHANGING VELOCITY
Resultant force meaning and example
Sum of all forces present, taking into account their direction. If its backwards, negative and if its forwards, positive.
For example, two people are pushing a block. The person pulling the block is pulling with a force of 5N and the person pushing is pushing with a force of 10N. The friction is -3N (going backwards so negative) What is the resultant force?
= 10 + 5 -3 = +12N
IF POSSIBLE PUT PLUS OR NEGATIVE
Newton’s second law
Definition - Resultant forces make things accelerate
Friction and air resistance
What direction and does it get bigger
As we know, air resistance acts in a upwards force, this is because air resistance always acts in the opposite way to motion.
Same goes for friction, the opposite way to motion.
Friction and air resistance gets bigger as you move faster
Newton’s first law
Not accelerating meaning
Definition - If there is no resultant force, things don’t accelerate
Not accelerating might mean staying still but can also mean carrying on in a straight line at a steady speed. This is Uniform Motion
For example, a person is pushing with a force of 10N and another person is pushing with a force of -10N. The resultant force is 0N and so they are moving at a steady speed or staying still.
Balanced and unbalanced forces, example with shuttlecock and when an object is with her for example a parachute and without a parachute
Terminal velocity
Hot air balloons
When a shuttlecock is dropped, it will accelerate at first because the forces are unbalanced (the downwards force, weight/gravity, and the upwards force, air resistance) and the resultant force is ‘not zero.’ So it will accelerate because of Newton’s 2nd Law which says resultant forces make things accelerate. However, the forces will start to become balanced and the resultant forces becomes zero and so will reach a steady speed because of Newton’s first law which states ‘if there is no resultant force, things don’t accelerate.’
If there is something on her, meaning a parachute, the steady speed will lower because the friction force os bigger because her surface area is bigger and the terminal velocity is reached when the forces are balanced but at a slower rate.
Without a parachute, the terminal velocity would be reached sooner because she doesnt have a bigger downwards force on her and will be reached when the forces become balanced.
There is also a force called upthrust, which happens in spite of the pull of gravity
Terminal velocity is the maximum speed, can’t accelerate anymore
Acceleration
Acceleration (m/s^2) = Resultant force (Newton) / Mass (kg)
Triangle - Resultant force at the top, left is mass and right is acceleration
If there is no resultant force, there is no acceleration. This means that the object will carry on moving at the same velocity which might be zero if it was already at that.
Braking distance
The distance that a car will travel while the breaks are applied
Proportional and inversely proportional lines on a graph (acceleration against force) for proportional and acceleration against mass for inversely.
If the graph shows a straight line passing through the origin, it shows that the force is proportional to the acceleration. So doubling the force acting on the object will double the acceleration, this is when the mass is the same.
If the mass is varied, acceleration against mass, the acceleration is inversely proportional to the mass. So doubling the mass of the object will halve the acceleration.
What factors might there be in a van’s design that will limit its speed
Shape of front - big surface area so the air resistance is large and so it will slow down
Maximum thrust of engine - bigger thrust will allow a bigger speed before the forces are balanced
Lower friction components - reduces friction so will reach a higher speed before the forces are balanced.
How might a car be designed to have a higher top speed?
Streamline shape - gives it a lower air resistance
Powerful engine - gives it a larger thrust force
Very low friction components - less friction so will move at a higher speed until forces are balanced.
The gravitational field strength of the Moon and the Earth
Uses the symbol g
Earth - 10N/kg
Moon - 1/6N/kg
