Chapter 1) Motion, forces, and energy

How is length measured?

Using a ruler.

What is the unit of length?

Metres, m.

How can you find the volume of a regular solid?

By calculation. ●Use a ruler to measure dimensions ●Use an appropriate equation to calculate volume

How can you find the volume of an irregular solid?

By submersion. ●Fill a measuring cylinder with water and read initial volume ●Submerge the object (hold down if necessary) and measure final volume ●The change in volume = volume of object

How can time be measured?

Using clocks or stopwatches.

How can the accuracy of measurements be increased?

increased? By taking multiple measurements and calculating an average.

How can very small distances be measured? (supplement)

(supplement) Using a micrometer screw gauge.

What is a scalar quantity? (supplement)

A quantity with magnitude only.

What is a vector quantity? (supplement)

A quantity with magnitude and direction.

What is a resultant vector? (supplement)

A single vector demonstrating the combined effect of all separate vectors.

How can vectors at right angles to one another can be combined into one resultant vector? (supplement)

be combined into one resultant vector?(supplement) Graphically (by drawing each to scale) or by calculation (using pythagoras and trigonometry).

What are the 3 main components of motion?

1. Speed 2. Direction 3. Acceleration (change in speed)

Give the equation for average speed.

average speed (m/s) = distance (m) ÷ time (s) speed distance time

What is the difference between speed and velocity?

●Speed is scalar, so doesn’t include direction. ●Velocity is a vector, so is the speed of movement in a certain direction.

Give the equation for velocity.

velocity (m/s) = displacement (m) ÷ time (s) v = s ÷ t v s t

What is the difference between distance and displacement?

displacement? ●Distance is scalar, so doesn’t include direction. ●Displacement is a vector; the distance travelled in a certain direction.

Give an equation for acceleration. (supplement)

acceleration = final velocity

What is the gradient of a displacement

time graph?

What does a curved line represent on a displacement

time graph?

What is deceleration? (supplement)

Negative acceleration (slowing down, decreasing speed).

What does a horizontal line represent on a displacement

time graph?

How can velocity be calculated from a displacement

time graph?

What does the gradient of a velocity

time graph represent?

What does the area under a velocity

time graph represent?

What does a curved line represent on a velocity

time graph?

What does a speed

time graph look like when an object is moving with changing speed (accelerating)?

What does a positive gradient represent on a velocity

time graph?

What does a negative gradient represent on a velocity

time graph?

What state is an object in when the Y axis is at 0 on a velocity

time graph?

What is the value of acceleration due to gravity at the Earth’s surface?

the Earth’s surface? The acceleration of free fall = 9.81 m/s²

What conditions are needed for an object to fall with the constant acceleration of ‘g’?

the constant acceleration of ‘g’? They must be free falling in a uniform gravitational field in the absence of air/liquid resistance.

Explain how terminal velocity is reached. (supplement)

●Initially, the only force is weight so acceleration is 9.8m/s2 ●As it accelerates, speed increases, which increases air resistance. ●This decreases the resultant force (downwards), so acceleration decreases. ●Eventually, weight and air resistance are equal and opposite, so there is no resultant force, no acceleration, and terminal velocity is reached.

Define mass.

The amount of matter contained in an object.

Define weight.

The gravitational force acting on an object with mass.

Give the equation for weight, including all SI units.

Weight (N) = mass (kg) x gravitational field strength (kg/N)

What does ‘g’ represent?

The gravitational field strength.

How can weight and mass be compared?

Using a balance, which measures weight and can converts it into mass (by dividing by ‘g’).

How does an object’s mass and weight differ from planet to planet? (supplement)

planet to planet?(supplement) ●Mass does not change ●Weight differs because it is the effect of the gravitational field on a mass, and ‘g’ is different at the surface of different planets.

State the equation for density. Give appropriate units.

units. density (kg/m³) = mass (kg) ÷ volume (m³) ρ = m/v

Describe a method to determine the density of a regular solid.

regular solid. ●Take measurements of relevant dimensions using a ruler ●Calculate the volume using an appropriate equation ●Measure mass using a balance and calculate density using ρ = m/v

Describe a method to determine the density of an irregular solid.

irregular solid. ●Measure volume by submersion: read the volume of liquid, submerge the solid, then read the change in volume (= volume of object) ●Measure mass using a balance ●Use ρ = m/v to calculate density

Describe a method to determine the density of a liquid.

liquid. ●Place an empty beaker on top of a balance and zero the device ●Pour liquid into the beaker to determine the mass ●Pour the same liquid into a measuring cylinder and read off the volume ●Use ρ = m/v to calculate density

What is the density of water?

1g/cm3

When do objects float in water?

When the object is less dense than water.

When do objects sink in water?

When the object is more dense than water.

If liquids do not mix, which will sink below the other? (supplement)

(supplement) The liquid which has the highest density.

What effects can a force have on an object?

A force can alter shape and size, or speed and direction.

How can the effect of force on an elastic objects shape (specifically its extension) be investigated?

shape (specifically its extension) be investigated? ● An object’s initial length is measured with a ruler. ● Masses are attached to the object incrementally. ● The object’s length is measured and recorded after the addition of each. ● Extension = new length

What is the spring constant (plus the equation to calculate it)? (supplement)

calculate it)? (supplement) The force required per unit of extension. spring constant = force applied / extension units = N/m

At what point does the equation for the spring constant no longer apply? (supplement)

constant no longer apply? (supplement) The limit of proportionality.

What does the limit of proportionality look like on an extension

load graph? (supplement)

Define ‘resultant force’.

A single force with the same effect as the sum of all the individual forces acting on an object (taking into account direction).

What happens if a resultant force acts on an object?

It causes a change of momentum in the direction of the force.

How can a resultant force change the motion of an object?

object? It can change an object’s velocity either by changing its… ●Speed ●Direction

How can the resultant force be found from forces acting along the same straight line?

acting along the same straight line? Sum of all forces acting in one direction

How can the resultant force be found from forces acting at right angles to one another?

acting at right angles to one another? Graphically (by drawing each to scale) or by calculation (using pythagoras and trigonometry).

What happens if there is zero resultant force?

The object will remain stationary, or (if moving) will continue to move in the same direction with the same speed.

How is acceleration related to the resultant force acting on an object and its mass? (supplement)

acting on an object and its mass? (supplement) Acceleration is proportional to the resultant force acting on it and inversely proportional to the object's mass. force=mass × acceleration F=ma

In terms of a resultant force, how do objects move in a circular motion? (supplement)

a circular motion? (supplement) A resultant force continually acts perpendicular to the object’s direction of motion, enabling velocity to be constantly changing (always changing direction).

What will happen to an object in circular motion if force increases but mass and radius are constant? (supplement)

force increases but mass and radius are constant? (supplement) Its speed will increase.

What will happen to an object in circular motion if force increases but mass and speed are constant? (supplement)

force increases but mass and speed are constant? (supplement) The radius of its circular motion will decrease.

What will need to happen for an object in circular motion to maintain a constant radius and speed if force increases? (supplement)

motion to maintain a constant radius and speed if force increases? (supplement) The force must increase.

Define friction.

Friction is the force providing resistance to the motion of two surfaces sliding past each other.

Give an example of a frictional force.

Air resistance.

What is a pivot point?

The point at which an object can rotate about.

If force is applied in the same line as the pivot, what happens to the object?

happens to the object? The object will not rotate, and remains stationary.

What is a moment?

The rotational (or turning) effect of a force.

Give the equation for moments.

moment (Nm) = force (N) x distance (m) (note: distance is the perpendicular distance from the force to the pivot)

When does rotational equilibrium occur?

When the sum of clockwise moments = the sum of anticlockwise moments This is the principle of moments.

What is a centre of gravity?

A single point through which the force of an object’s weight acts. (This is a modelling assumption).

Describe how to find the centre of gravity of a plane lamina.

lamina. ●Hang up the lamina and suspend a plumb line (thread) from the same place. ●Mark the position of the plumb line. ●Repeat with the lamina suspended from different places. ●Where these lines intersect is the centre of gravity.

How does the position of the centre of gravity affect the stability of an object?

the stability of an object? ●If the centre of mass is below the point of suspension of an object, it will be in stable equilibrium. ●If the centre of mass is above the point of suspension of an object, it will be in unstable equilibrium. ●If the line of action of the object’s weight moves outside the base, it will topple.

Give the equation for momentum, including units (supplement)

(supplement) Momentum (kgm/s) = mass (kg) x velocity (m/s)

Give the equation for impulse, including units. (supplement)

(supplement) Impulse = force x time for which force acts =∆(mv) Where ∆(mv) is the change in momentum.

What is the principle of conservation of momentum? (supplement)

(supplement) Momentum is always conserved in an explosion/collision, so there is no net change in momentum. Momentum before = momentum after (provided there are no external forces).

Give seven examples of the different forms in which energy can be stored?

energy can be stored? ●Kinetic ●Gravitational potential ●Chemical ●Elastic (strain) ●Nuclear ●Electrostatic ●Internal (thermal)

What type of energy is stored in a moving object?

Kinetic energy.

What happens, in terms of energy, when an object is lifted?

lifted? Its gravitational potential energy increases.

Give an equation for kinetic energy (supplement)

kinetic energy (J) = ½ x mass (kg) x velocity² (m/s) E = ½mv²

Give an equation for gravitational potential energy (supplement)

(supplement) Gravitational potential energy (J) = mass (kg) x height (m) x gravitational field strength (N/kg) E = mgh

Give an equation for change in gravitational potential energy (supplement)

energy (supplement) change in gravitational potential energy = mass x gravitational field strength x change in height ∆E p = mg∆h

Give four ways through which energy can be transferred.

transferred. ●Forces ●Electrical currents ●Heating ●Waves (electromagnetic/ sound)

What is the law of conservation of energy?

●Energy is neither created nor destroyed. During an energy transfer: Total energy before the event = total energy after the event

How can energy transfer be shown using diagrams?

Flow diagrams

Define work done.

●Work is done on an object when energy is transferred (from one form to another) ●Equal to the product of force and distance

Give the equation for work done

work done (J) = force (N) x distance (m) W = Fd (where distance is the distance moved along the line of action of the force)

What are the main energy resources available to humans?

humans? ●Fossil fuels ●Nuclear fuels ●Biofuels ●Water (hydroelectricity, tides, and waves) ●Solar energy (solar panels and cells) ●Wind

What factors need to be considered when thinking about the advantages and disadvantages of each energy resource?

about the advantages and disadvantages of each energy resource? ●Renewability ●Availability ●Reliability ●Scale ●Environmental impact

Define renewable energy.

Energy from a source which does not run out, so can be replenished.

Which energy sources are non

renewable?

Which energy sources are renewable?

●Biofuels ●Wind ●Hydroelectric and tidal energy ●Geothermal energy ●Solar power

Are non

renewable or renewable energy resources usually better at providing electricity on a large scale?

How can electricity be generated from different energy sources?

energy sources? ●A turbine is turned using energy from an energy resource. ●The turbine turns coils, in a magnetic field, in a generator. ●This generates electrical power.

How are biofuels and fossil fuels used to generate electricity?

electricity? They are burnt to generate electrical power: ●Their chemical energy is transferred to heat energy. ●The heat energy is used to boil water, creating steam. ●The steam turns the turbine.

How are nuclear fuels used to generate electricity?

They undergo nuclear fission to generate electrical power: ●Heat energy is released by nuclear fission. ●The heat energy is used to boil water, creating steam. ●The steam turns a turbine.

How is water used to generate electricity?

Water’s waves and tides can be used: ● The kinetic energy as waves and tides move is used to turn underwater turbines. OR hydroelectric dams can be used: ● The water behind the dam is above ground level, so has gravitational potential energy. ● This energy is transferred to kinetic energy when water is released down a slope. ● The flowing water turns the turbine.

How are radioactive elements used to generate electricity?

electricity? ● As radioactive elements decay, their geothermal energy heats the surrounding rock. ● Water is poured into shafts in the hot rock. ● The heat energy boils the water, creating steam, which is returned via another shaft. ● Steam turns a turbine.

How can the sun be used to generate electricity?

Solar energy from sunlight is turned into an electrical current by solar cells.

How can the sun be used to heat water?

●Infrared waves of the Sun’s light heat water, contained within solar panels. ●The water goes to a tank and is stored for later use. ●A boiler may be needed to heat the water further.

How can the wind be used to generate electricity?

As the wind blows, it transfers kinetic energy to the blades of wind turbines.