Forces

Question 1

What is a scalar quantity?

Answer 1

. A quantity that only has a magnitude
. A quantity that isn’t direction
dependent

Question 2

What is a vector quantity?

Answer 2

A quantity that has both a magnitude
and an associated direction.

Question 3

How can a vector quantity be drawn and what does
it show?

Answer 3

. As an arrow
. The length of the arrow represents the
magnitude
. The arrow points in the associated
direction

Question 4

What is a force?

Answer 4

A push or pull acting on an object due to
an interaction with another object.

Question 5

What are the two categories that all forces can be
split into?

Answer 5

1. Contact forces (objects touching)
2. Non-contact forces (objects separated)

Question 6

Give three examples of contact forces.

Answer 6

1. Friction
2. Air resistance
3. Tension

Question 7

Give three examples of non-contact forces.

Answer 7

1. Gravitational forces
2. Electrostatic forces
3. Magnetic forces

Question 8

Is force a vector or a scalar quantity?

Answer 8

· Vector
. It has both a magnitude and an
associated direction

Question 9

Give three examples of vector quantities.

Answer 9

1. Velocity
2. Displacement
3. Force

Question 10

Give three examples of scalar quantities.

Answer 10

. Temperature
· Time
· Mass
. Speed
. Distance
· Energy

Question 11

What is weight?

Answer 11

The force that acts on an object due to
gravity and the object’s mass.

Question 12

What quantities does weight depend on?

Answer 12

Weight = mass x gravitational field strength

. The object’s mass
. The gravitational field strength at the
given position in the field

Question 13

What is the unit used for weight?

Answer 13

The Newton (N).

Question 14

What is the unit used for gravitational field strength?

Answer 14

N/kg

Question 15

What is meant by an object’s centre of mass?

Answer 15

The single point where an object’s
weight can be considered to act through.

Question 16

What piece of equipment can be used to measure
an object’s weight?

Answer 16

A calibrated spring-balance or newton-
meter.

Question 17

What is the name given to the single force that is equivalent to all the other forces acting on a given
object?

Answer 17

The resultant force

Question 18

What does it mean if a force is said to do ‘work’?

Answer 18

The force causes an object to be
displaced through a distance.

Question 19

What is the equation used to calculate work done?
Give appropriate units.

Answer 19

Work done = Force x Distance

Work done (Joules), Force (Newtons),
Distance (metres)

Question 20

What distance must be used when calculating work
done?

Answer 20

It must be the distance that is moved
along the line of action of the force.

Question 21

Under what circumstance is 1 joule of work done?

Answer 21

When a force of 1 Newton causes a
displacement of 1 metre.

Question 22

How many Newton-metres are equal to 1 joule of
energy?

Answer 22

1 Nm= 1J

Question 23

How much work is done by the force
acting on the below object over a
distance of 5m?

Answer 23

10 N
<——— (square)

Question 24

How much work is done by the force acting on the
below object over a distance of 5m?

Answer 24

10 x 5 = 50 Nm

= 50 J

Question 25

What occurs when work is done against frictional forces?

Answer 25

· A rise in temperature of the object occurs . Kinetic energy is converted to heat

Question 26

Why does air resistance slow down a projectile?

Answer 26

. The object does work against the air resistance . Kinetic energy is converted in to heat, slowing down the object

Question 27

Explain the relationship between the force applied and the extension of an elastic object.

Answer 27

The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded.

Question 28

What is meant by an inelastic deformation?

Answer 28

. A deformation which results in the object being permanently stretched . The object doesn't return to its original shape when the force is removed

Question 29

State the equation relating force, spring constant and extension. Give appropriate units.

Answer 29

Force = Spring Constant x Extension Force (N), Spring Constant (N/m) Extension (m)

Question 30

What type of energy is stored in a spring when it is stretched?

Answer 30

Elastic potential energy.

Question 31

What can extension be replaced with in the equation for spring force?

Answer 31

Compression.

Question 32

What is an alternative name for the turning effect of a force?

Answer 32

A moment.

Question 33

State the equation used to calculate the moment of a force. Give appropriate units.

Answer 33

Moment of force = Force x Distance Moment (Nm), Force (N), Distance (m)

Question 34

What distance measurement is used when calculating a moment?

Answer 34

The perpendicular distance from the pivot to the line of action of the force.

Question 35

If an object is in equilibrium, what can be said about the moments acting on the object?

Answer 35

The clockwise moments are equal to the anticlockwise moments.

Question 36

What three parts make up a lever system?

Answer 36

1. Load 2. Effort 3. Pivot

Question 37

How can a lever be used as a force multiplier?

Answer 37

If the distance between the effort and pivot is greater than the distance between the pivot and load, the force applied on the load is greater than the effort force. This is since the moment on both the effort and load must be the same.

Question 38

Give an example of when a lever may be used to multiply a force.

Answer 38

A wrench, which has a long handle so that the force applied by the user is multiplied.

Question 39

What determines the moment of a gear wheel?

Answer 39

The size of the wheel

Question 40

What is meant by the term 'fluid'?

Answer 40

A liquid or a gas.

Question 40

Describe the moment and speed of a larger gear being driven by a smaller gear.

Answer 40

The larger wheel will rotate more slowly but will also produce a larger moment.

Question 41

In any fluid, at what angle do the forces due to pressure act on a given surface?

Answer 41

At right angles (normal to) the surface.

Question 42

State the equation used to calculate pressure. Give appropriate units.

Answer 42

Pressure = Force/Area Pressure (Pascals), Force (Newtons), Area (metre2)

Question 43

What happens to the density of the atmosphere with increasing altitude?

Answer 43

The atmosphere becomes less dense as altitude increases.

Question 44

Explain why atmospheric pressure decreases with an increase in height.

Answer 44

. Pressure is created by collisions of air molecules · The quantity of molecules (and so weight) decreases as the height increases · This means atmospheric pressure decreases with an increase of height

Question 45

What is the Earth's atmosphere?

Answer 45

A thin (relative to the magnitude of the Earth) layer of gas surrounding the Earth.

Question 46

How does pressure in fluids increase with depth?

Answer 46

As the depth increases, the mass of liquid above that depth also increases. This means that the force due to the mass increases. Since the force has increased whilst the area has remained constant, the pressure will increase.

Question 47

Why does pressure in fluids increase with density?

Answer 47

As the density of a fluid increases, the number of particles in a given volume increases. Consequently the weight of the fluid is greater. This means that the force from the fluid above a certain point is larger. Since the force has increased, the pressure also increases.

Question 48

What equation shows the magnitude of pressure in liquids at different depths?

Answer 48

Pressure due to a column of liquid(Pa) = Column height(m) x density(kg/m3) x gravitational field strength(N/kg) P = h(strange p)g

Question 49

Why are objects in a fluid subject to an upthrust?

Answer 49

When an object is submerged in a fluid, it has a higher pressure below it than it does above, as there is more weight above it at the bottom than there is at the top. This leads to an upwards force called upthrust. You float or sink depending on whether the upthrust is more or less than your weight.

Question 50

What is upthrust always equal to?

Answer 50

The weight of the fluid that the object displaces.

Question 51

What factors influence whether an object will sink or float?

Answer 51

. Upthrust · Weight . Density of fluid

Question 52

Explain why an object with a density greater than that of water can never float.

Answer 52

Upthrust is equal to the weight of the displaced fluid. If the density of the object is high, there would not be enough volume displaced to produce an upthrust larger than the object's weight. This means that it will sink.