P8 Flashcards
Describe a scalar
a quantity with only magnitude (size) and no direction
Examples of scalar quantities
- Distance
- Mass
- Time
- Speed
- Energy
Examples of vector quantities
- Displacement
- Velocity
- Acceleration
- Weight
- Momentum
- Force
What is a vector and how can they be represented
- A quantity with both magnitude and direction
- They can be represented by an arrow
- The length of the arrow is the magnitude
- The direction of the arrow is the direction of the vector
Examples of non-contact forces
- Gravitational force
- Electrostatic force
- Magnetic force
What is a force
A push or a pull that acts on an object due to the interaction with another object. It is a vector quantity
Examples of contact forces
- Tension
- Friction
- Air/water resistance
- Normal contact force
Equation to calculate weight
W = mg
Weight = mass x gravitational field strength
units of weight are newtons
What is the centre of mass
The point of an object at which its weight is considered to act
Experiment to find the centre of mass of a piece of card
- Put a hole in the card and suspend it on a clamp stand rod
- Use a plumbline to draw the direction of the force
- Repeat with different points
- Where the lines meet is the centre of mass
Equation for work done
- Worl=k done = force x distance
- W = Fs
What is hookes law and the equation for it
The extension of a spring is directly proportional to the force applied giving the limit or proportionality is not exceeded
equation - Force = spring constant x extension (F = ke)
How many forces are needed to stretch, compress or bend an object
- 2 for stretch and compress
- 3 for bend
- This means the forces are balanced
- If they weren’t, the elastic object would move instead
Experiment for force on an spring
- Set up a clamp stand with a weight on the bottom, a clamp and hang the spring from the clamp.
- Set up another clamp and a boss to fix a metre ruler alongside the spring
- Record the ruler reading tht is with the bottom of the spring and this is the intial length
- Hang a 1N weight onto the bottom of the spring and record the springs new length
- Calcualte the extension by doing extension = new length - intitial length
- Add further weights increasing by 1N each time
- For each new force/weight, find the new length of the spring and calculate the extension
- Plot a graph with changing extension and weight
What is deformation and what are the two types
- Deformation is a change in the shape of an object. More than one force is applied so it changes shape instead of moving
- The two types are elastic and inelastic deformation
What is the resultant force
A single force that has the same effect as all the original forces acting together
What is a moment
The turning effect of a force around a pivot
How are moments used in real life
- Wheelbarrows
- See-saws
- Crowbars
- Cranes
Equation to find the moment
- Moment (Nm) = Force (N) x Distance (m)
- M = fd
What can we say about the moments if an object is balanced
The sum of the anti-clockwise moments equals the sumn of the clockwise moments
Why does an object topple over
- The line of action from the centre of mass (the weight) is outside the base
- There is an unbalanced (resultant) moment acting on the block
- The object then topples
What do levers do to the turning effect of the force
- Transmit it to the other side of the pivot
- They are force multipliers so allow a froce to be applied further from the pivot
Defenition of inelastic deformation
Where an object is stretched of compressed and it doesn’t go back to its original shape once the forces have been removed
