Forces Flashcards
Define a scalar quantity and give 2 examples
It is a quantity which only has size or magnitude
eg a kg of apples or temperature of 30 degrees
Define a vector quantity
What type of quantities are vectors?
It is a quantity which has size or magnitude and direction
Forces are vector quantities because you can push with a force of 240N to the left or to the right
What is meant by the term velocity
It is a speed in a certain direction
What is the difference between speed and velocity
Speed is a scalar quantity and velocity is a vector.
if we say an aeroplane is travelling at 180m/s then we are describing it’s speed. If we say it’s travelling at 180m/s due east then we are describing it’s velocity.
What is the difference between distance and displacement?
Distance is a scalar quantity and displacement is a vector.
For example the distance from Thornbury Castle to Warwick castle is 71 miles. If we add a direction of NE then it becomes a displacement.
How is a vector drawn?
vectors are represented by arrows. The size of the arrow represents the magnitude of the vector and the direction is shown by the direction of the arrow.
For example if an object has 2 forces acting on it and one is bigger than the other the arrows will be different lengths. The arrows will show the direction of the force.
What is a force?
A force is a push or a pull. therefor it is a vector quantitty because it has magnitude and direction.
What are the three things that force can change? - give examples to illustrate your answers.
- Shape eg stretching a spring
- Speed eg throwing a ball increases it’s speed
- Direction eg batting a ball can change it’s direction
What is a contact force?
A contact force is one which can be exerted between two objects when they touch
eg your hand on a ball
What are the four main contact forces?
- Normal contact force, the force which supports an object resting on a surface eg your phone on a table.
- Friction, the force which opposes objects moving relative to each other eg the tyres on your bike and the road surface
- Tension the force exerted through a rope when we pull on it eg when towing a car
- Air resistance also called drag. It is the force acting on an object moving through the air. eg a car driving- you can feel it if you hold you hand out of the window.
What is a non contact force?
They are forces which act between objects which are physically separated.
Identify and describe 3 non contact forces.
- Gravitational. Gravity is the force which pull objects down towards the earth.
- Electrostatic. These forces act between charged objects eg when you rub a balloon and can stick it to a wall.
- Magnetic. Magnets attract objects made of iron or steel towards them.
What units are used to measure forces?
They are measured in newtons (N)
kilonewtons (kN) and meganewtons (MN) are used to measure large forces
Describe the term weight, how is it calculated?
Weight describes the pull of gravity on an object
It is calculated as W = mg
Weight = mass x gravitational field strength.
What is gravitational field strength?
The earth produces a gravitational field which pulls objects towards it. Near the surface this is 9.8 N/kg
What is the relationship between weight and mass
They are directly proportional, so if your mass decreases so does your weight.
Your weight changes if the gravitational field changes - so in space where there is a very low gravitational field your weight is less but your mass remains the same.
weight ∝ mass
What is the name of the point on an object through which the weight is considered to act.
The centre of mass
What is meant by the term resultant force
It is the single force which is a combination of all of the other forces acting on an object. It has the same effect as all of the forces acting together.
eg two people pushing an object, one pushes with a force of 300N the other 400N the resultant force is 700N
OR two teams pulling against each other on a tug of war rope, one pulls with a force of 2500N the other 2700N the resultant force is 200N
What is a free body diagram?
A diagram which shows the magnitude and direction of all of the forces acting upon an object. The forces act through a point, the centre of mass.
Resolving forces
If you are given a diagram with a vector and an angle.
1) Measure the length of the vector and calculate the scale used. Divide the number of cm by the number of Newtons to get a ratio
2) Complete the right angled triangle and measure the lengths of the horizontal and vertical sides.
3) From the scale calculate the forces. Multiply the length in cm by the ratio to get the answer in Newtons
How could you define the term work?
It is when a force acts on an object and causes it to move through a distance.
W = F x s
Work (J) = Force (N) x distance moved in the direction of the force (m)
Give some examples of how energy can be transferred during work
- Dragging a box along the floor is work and because you are working against the frictional forces of the ground the temperature of the floor and the box both rise.
- If you lift up an object and put it on a shelf you are doing work. The energy expended by your muscles is transferred to the object as gravitational potential energy.
What happens when you apply a single force to an object.
It could change it’s speed or direction.
How many forces do you need in order to change the shape of an object?
At least 2 forces are need to change the shape of the object. If those forces are balanced then the object will remain stationary.
If an object like a spring has been stretched and returns to its original length what is it called.
Elastic deformation.
What is inelastic deformation?
If an object like a spring has been stretched and does not return to its original length
What is the name given to the difference between the stretched and unstretched lengths of a spring
Extension
What is the equation used for elastic deformation
Force(N) = spring constant (N/m) x extension (m) F = k e
Explain the term spring constant
Spring constant tells us how stiff and difficult to stretch or compress a spring is. It is measured in N/m. So if a spring has a spring constant of 180N/m then it will take a force of 180 newtons to stretch or compress the spring 1 m
What is the equation used to calculate the work done when compressing or stretching a spring?
elastic potential energy(N) = 1/2 x spring constant(N/m) x extension² (m)
Ee = 1/2k e²
What is the definition of the term limit of proportionality
It is the point beyond which a spring will be permanently deformed.
Elastic deformation stops and inelastic deformation begins.
What type of energy does a stretched spring store?
Elastic potential energy
Explain how energy is converted when a drinks can is squashed.
If it is slightly squashed and only elastic deformation has occurred then elastic potential energy is stored in the can which is then used to pop the can back into shape. However once it has reached the limit of proportionality and the can is permanently deformed there is no elastic potential energy stored in the can. Work has been done as the atoms have been moved past each other to create a new shape. This work causes a small rise in temperature in the can.
What is elastic potential energy?
It is the type of energy stored in a stretched spring before it reaches its limit of proportionality.
