Physics - FORCES (P5)

Forces & Their Interactions -

What is a vector quantity?

A quantity that has both magnitude + direction.

Forces & Their Interactions -

What is a scalar quantity?

A quantity that has magnitude only.

Forces & Their Interactions -

Give three examples of vector quantities.

Force, velocity, displacement.

Forces & Their Interactions -

Give three examples of scalar quantities.

Speed, distance, mass.

Forces & Their Interactions -

What is a force?

A push / pull on an object due to interaction w/ another object.

Forces & Their Interactions -

What is the unit of force?

Newton (N).

Forces & Their Interactions -

What is a contact force?

A force that acts when objects are physically touching.

Forces & Their Interactions -

What is a non-contact force?

A force that acts at a distance.

Weight & Mass -

What is the equation linking weight, mass, + gravitational field strength?

W = mg

weight = mass x gravitational field strength

Weight & Mass -

What are the units for weight, mass, + gravitational field strength?

Weight: Newtons (N)

Mass: Kilograms (kg)

Gravitational field strength: N/kg

Weight & Mass -

What is the value of gravitational field strength on Earth?

9.8 N/kg

Resultant Forces & Free-Body Diagrams -

What is a resultant force?

A single force that has the same effect as all the forces acting on an object combined.

Resultant Forces & Free-Body Diagrams -

What does a free-body diagram show?

All the forces acting on an object + their direction.

Resultant Forces & Free-Body Diagrams -

What happens if the resultant force on an object is zero?

The object is at rest / moving at constant velocity.

Work Done & Energy Transfer -

What is the equation for work done?

W = Fs

work done = force x distance

Work Done & Energy Transfer -

What are the units for work done, force, + distance?

Work: joules (J)

Force: newtons (N)

Distance: metres (m)

Work Done & Energy Transfer -

What does it mean if work is done against friction?

Energy is transferred to the thermal store, usually causing heating.

Forces & Elasticity -

What is Hooke’s Law?

The extension of a spring is directly proportional to the force applied, up to the limit of proportionality.

Forces & Elasticity -

What is the equation linking force, spring constant, + extension?

F = ke

force = spring constant x extension

Forces & Elasticity -

What do the symbols F = ke represent?

F: force (N)

k: spring constant (N/m)

e: extension (m)

Forces & Elasticity -

What is the limit of proportionality?

The point beyond which extension is no longer proportional to force.

Forces & Elasticity -

What is the equation for elastic potential energy?

E = 1/2ke(squared)

Required Practical: Stretching a Spring -

In the spring practical, what variables are measured?

Force applied + extension of the spring.

Required Practical: Stretching a Spring -

How do you calculate the spring constant from a graph?

From the gradient of the force-extension graph (in the linear region).

Moments, Levers, & Gears -

What is the equation for the moment of a force?

Moment = F x d

Moments, Levers, & Gears -

What do the symbols in the moment equation represent?

F: force (N)

d: perpendicular distance from the pivot (m)

Moments, Levers, & Gears -

What is the principle of moments?

For an object in equilibrium, the total clockwise moment = total anticlockwise moment.

Moments, Levers, & Gears -

How do levers + gears make work easier?

They increase the distance over which a force acts, reducing the force needed.

Pressure in Fluids -

What is the equation for pressure in a fluid?

p = F/A

pressure = force/area

Pressure in Fluids -

What is the equation for pressure at a depth in a liquid?

p = hpg

pressure = height of liquid x density of liquid x acceleration due to gravity

Pressure in Fluids -

What do the symbols in p = hpg mean?

p: pressure (Pa - pascals)

h: height (m)

p: density (kg/m(cubed))

g: gravitational field strength (N/kg)

Pressure in Fluids -

Why does pressure increase w/ depth in a liquid?

There is more weight of liquid above acting downwards.

Forces & Motion -

What is Newton’s First Law?

An object remains at rest / moves at constant velocity unless acted on by a resultant force.

Forces & Motion -

What is Newton’s Second Law?

F = ma

resultant force (N) = mass (kg) x acceleration (m/s(squared))

Forces & Motion -

What is Newton’s Third Law?

Every action has an equal + opposite reaction.

Forces & Motion -

What factors affect stopping distance?

Thinking distance + braking distance.

Forces & Motion -

Name two factors that affect braking distance.

Road conditions, brake condition, tyre quality, mass of vehicle.

Forces & Motion -

Name two factors that affect thinking distance.

Tiredness, alcohol/drugs, distraction.

Motion Graphs -

What does the gradient of a distance-time graph represent?

Speed.

Motion Graphs -

What does the gradient of a velocity-time graph represent?

Acceleration.

Motion Graphs -

What does the area under a velocity-time graph represent?

Distance travelled.

Motion Graphs -

What is the equation for acceleration?

a = v-u/t

acceleration (m/s(squared)) = final velocity (m/s) - inital velocity (m/s) / time (s)