P5 (part 1) Flashcards
What is a scalar quantity + example?
it is a quantity with a magnitude (size) only
example: mass, speed, volume, energy, time, distance and power
What is a vector quantity + example?
it is a quantity with a magnitude and an associated direction
example: forces , displacement, acceleration and velocity
How are vectors represented?
by an arrow. The length of the arrow represent the size and the direction of the arrow represents the direction of the vector
What is a force?
is a ‘push’ or ‘pull’
How can forces be categorised?
contact or non-contract
What are examples of contact force?
- friction
- air resistance
- tension
- normal contact force (reaction force)
What are examples of non-contact force?
- gravitational force (weight)
- electrostatic force
- magnetic force
Why are forces considered to be vectors?
they have both a size and direction
What are the summary of common forces?
acting down :
- weight
acting up :
- lift, normal reaction force, upthrust (buoyancy)
acting to cause forward motion:
- thrust
acting to oppose forward motion:
- friction, air/water resistance tension
What is mass?
the amount of matter an object can contain
What is mass measured in?
kg
Why is weight a vector?
it has a magnitude and a direction
What is weight?
is the force acting on an object due to gravity
What causes the force of gravity around the Earth?
because the Earth is massive( it has alot of mass in physics)
What are the units of weight?
newtons (N)
What do we mean when we say mass and weight are ‘directly proportional’?
if the mass of an object doubles so will the weight
the relationship between mass and weight are ∝
Why can weight change?
because it depends on the strength of gravity
How can we calculate the weight of an object?
weight (N) = mass (kg) x gravitational field strength (m/s)
W= mg
How can we measure the weight of an object?
- scale/balance
- or a newton meter
What is the centre of mass of an object?
is defined as ‘the point at the weight of an object can be considered to act
What is meant by the ‘resultant force’?
is a single force that can replace all of the other forces acting on something
What can happen to an object if the forces acting on it are unbalanced?
- it can speed up
- it can slow down
- it can change direction
How about if the forces are balanced?
- stays at rest (if it’s already not moving)
- move at a constant speed in the same direction (if it’s already moving)
What is work done?
when a force makes an object move a certain distance
What is another way of saying work done?
energy transferred
What is the unit of work done?
joules (J)
During a race, a car brakes can glow red hot. Explain why, using ideas about work
- when the driver presses the brake the force of friction acts on the brake disk
- this force doesn’t work on the car, causing it to slow down or stop
- as work is being done, energy is transferred from the kinetic store of the car to the thermal store of the brakes causing them to glow red hot
What is the equation for work done?
work = force x distance moved
W = fs
What is the alternative unit for work done?
newtons meters (Nm)
1Nm = 1J
What are the 4 energy equation?
Ep = mgh Ek = 1/2mv2 E = Pt E = QV
When a force is applied to an object, what 3 thing can happen?
the object can:
- bend
- stretch
- compress
More than one force needs to be acting. Why?
more than one force needs to be acting, otherwise the object would simply move in the direction of the force applied
What are the 2 types of deformation?
- elastic
- inelastic
What happens in elastic deformation?
an object that goes back to its original shape after a force has been removed has been elastically deformed
What happens in inelastic deformation?
an object that does not go back to its original shape after a force has been removed has been inelastically deformed
What is meant by the ‘elastic limit’?
if a spring is stretched until it permanently deforms, we say it has reached its elastic limit
What is the equation for Hooke’s Law?
force (N) = spring constant (N/m) x extension (m)
F = Ke
What is the limit of proportionality?
the point at which the spring will no longer return to its original length
What happens to a spring once it is stretched beyond this point(its elastic limit)?
it is permanently deformed
How can you see where the limit of proportionality is from a graph of force against extension?
when the line starts to curve
What happens to the the energy to an object when work is done?
energy will be transferred to the elastic potential energy store of the object
What happens to the the energy to an object when it is elastically deformed?
then all of this energy is transferred to the object elastic potential energy store
What is the definition for elastic potential energy?
the amount of energy stored in a spring
What is the formula for elastic potential energy?
elastic potential energy (J) = 0.5 x spring constant (N/m) x extension2 (m)
Ee = 0.5ke2
