Forces and motion Flashcards
Length and volume
- Ruler is used to measure length for short distances
- Volume= LWH (length x width x height)
- To measure irregular shape volumes you have to put the object into a measuring cylinder water. It then displaces the water, making the water level rise by an amount equal tot he volume of the object.
- Micrometer can be used to measure distances that are too small to be used with a ruler
Time
- An interval of time is measured by a clock or stopwatch
- The period T of a pendulum is the time it takes to complete on oscillation
- If you have multiple time values, find the mean average
Speed
- Speed is the distance an object moves in a specific time frame (like one mile per hour). It is measured in m/s or km/h or mph
- It is a scalar quantity which is a quantity that only has a magnitude, therefore has to be positive
What is a vector quantity
It has a direction as well as magnitude, for example velocity (which can be negative or positive)
Speed equation
Speed = Distance/ time Time= Distance/ speed Distance= speed x time
Acceleration equation
Change in velocity
______________
Time taken
-Measured in m/s²
Distance/ time graph
- Gradient of graph is speed
- As speed is constant the gradient must not change (must be horizontal line)
Speed/ time graph
- Gradient of line tells us acceleration
- An increase in speed is a positive acceleration and a decrease is negative
- If acceleration is not constant, line will be curved
Forces
A force is a push/pull of one body on another. There are many different kinds of forces like:
- Friction, normal reaction force, gravitational force/ weight, air resistance/ drag, upthrust/ buoyancy
- A force may produce a change in size and shape of body, give an acceleration or deceleration or a change in direction depending on the direction of the force
Friction
A force that opposes motion. Occurs when 2 surfaces try and slide over each other
Normal reaction force
Opposing force from a surface when one object is in contact with another
Gravitational force
The pull of the Earth on an object
Air resistance/ drag
A force that opposes the movement of objects int he air
Upthrust/ buoyancy
An upward push on an object floating in a fluid e.g a boat on water
What are forces measured in
Newtons
Relationship between force, mass, acceleration
F= M x A A= F/ M M= F/ A
Force is a … quantity
A vector quantity
Direction of force
->5 + ->5 = -> 10
5-> +
Mass and weight
-Mass is the property of an object that is a measure of its inertia (a resistance to acceleration), the amount of matter it contains and its influence in a gravitational field
-Weight is the force of gravity acting on an object, measured in newtons (N) and given by the formula:
W=MG (Weight= mass x gravity)
Hooke’s law
- “Load force is directly proportional to extension provided that it is within its elastic limit”
- Elastic behaviour is the ability of a material to recover to its original shape after the forces causing deformation have been removed
- Once the spring has been stretched beyond its elastic limit, it will change shape permanently and will not return to its original shape (becomes plastic)
Formula for Hooke’s law
Force= force constant x extension / F=kx Extension= current length- original length
Key terms
- Limit of proportionality: point at which load and extension are no longer proportional
- Elastic limit: point at which the spring will not return to its original shape after being stretched
- Force constant (K) tells you how stiff the spring is
Spring arrangements
- Springs can be connected in series (end to end) or parallel (side by side)
- Springs in parallel share the load and so extend half as much
- An arrangement of two identical springs in series will halve the force constant (half as stiff)
- Two parallel springs will double the force constant (twice as stiff)
Centre of mass
- An imaginary point in a body (object) where the total mass of the body can be thought to be concentrated to make calculations easier
- For regular shaped, uniform objects, the centre of mass will be in the middle. It can be found by drawing lines of symmetry
- To find centre of mass on a flat irregular object:
- Get a flat object, get a Stan and a plumb line, punch 2 holes in your object, hang your object from the hole and attach the plumb line to the same hole, draw a vertical line where the plumb line is and repeat step four on the other hole
- Where the lines cross is the centre of mass
- Objects with a low centre of mass are stable as they are difficult to knock over
Pressure equation
P= F/A
