Forces and Motion

Question 1

What is a force?

Answer 1

Any interaction that, when unopposed, will change the motion (speed or direction) of an object.

Question 2

What is weight?

Answer 2

A force that pulls an object with mass downwards towards the centre of a planet.

Question 3

What is tension?

Answer 3

A force that is transmitted through a string, rope or cable.

Question 4

What is friction?

Answer 4

A surface force that opposes motion. It will cause an object to decelerate or become stationary.

Question 5

What is reaction?

Answer 5

A force that acts in the opposite direction to an action force, e.g. weight and its reaction (which, in some cases, is lift) or thrust and air resistance.

Question 6

What is lift?

Answer 6

A force caused by a fluid (gas or liquid) flowing over the surface of an object causing a difference in pressure and making it rise.

Question 7

What is thrust?

Answer 7

A force that causes an object to move or accelerate forward.

Question 8

What is air resistance?

Answer 8

A type of frictional force caused by air pushing against a moving object. The object’s surface area affects the magnitude of the air resistance.

Question 9

What is upthrust?

Answer 9

The upward force that a fluid (gas or liquid) exerts on a body floating in it.

Question 10

What is the elastic force?

Answer 10

A force that acts to return a stretched object to its original or natural shape/length.

Question 11

What is magnetism?

Answer 11

A force that acts between two magnetic objects. Depending on the poles of the magnets, it can either attract or repel the other object (opposite poles attract while like poles repel)

Question 12

What is the difference between vectors and scalars?

Answer 12

A scalar has only magnitude/size, whereas a vector has both size and direction. Forces are vectors that are defined using both size and direction.

Question 13

How are force diagrams drawn?

Answer 13

Refer to physical flashcard.

Question 14

What effect will a force have on an object?

Answer 14

A force can cause an object to accelerate, decelerate, become stationary or move at a constant speed.

Question 15

How are forces’ sizes defined?

Answer 15

In Newtons, N — the SI unit for force.

Question 16

How are forces’ directions defined?

Answer 16

Arrows can be drawn on diagrams, but in speech/writing, the force can be stated to act in a push or pull direction (or up/down or left/right).

Question 17

What is resultant force? and its formula?

Answer 17

The overall combined force acting on an object.

Fr = ma

‘F’subscript’r’ = resultant force 
m = mass
a = acceleration

Question 18

How is resultant force calculated?

Answer 18

By summing the forces acting on an object, taking their direction into account.
OR
Multiply the mass by the acceleration.

Question 19

What will a positive resultant force cause to happen an object? a negative resultant force? one of zero?

Answer 19

A positive resultant force will cause acceleration in the direction of the larger force (e.g. if upthrust is 10N and air resistance is 5N then resultant force is 5N (accelerating) upwards). A negative one will cause deceleration, while one of zero will cause an object to remain stationary or move at a constant speed, depending on what the object was doing.

Question 20

What is Newton’s first law of motion?

Answer 20

‘An object remains stationary, or moving at a constant speed, unless acted upon by a resultant force, in which case it will accelerate or decelerate.’

Balanced forces (resultant forces of 0) will cause an object an rest to remain at rest and a moving object to move at a constant speed.

Unbalanced forces will cause objects to accelerate or decelerate.

Question 21

What is Newton’s second law of motion?

Answer 21

‘The acceleration of an object of constant mass is directly proportional to, and in the direction of, the applied force.’

Resultant force formula applies.

Question 22

What are the units for mass and acceleration?

Answer 22

mass = kg

acceleration = m/s^2

Question 23

What is the formula for speed? density? pressure? weight? and their units?

Answer 23

speed = distance/time (s = d/t) (m/s)
t = d/s (s)
d = st (m)

density = mass/volume (d = m/v) (g/cm^3)
v = m/d (cm^3)
m = dv (g)

pressure = force/area (p = f/a) (N/cm^2)
a = f/p (cm^2)
f = ap (N)

weight (N) = mass x acceleration due to gravity (m/s^2)
(this is related to Fr = ma)

Question 24

What is the definition of distance? speed? time?

Answer 24

Distance is the length between two places.
Speed is the rate of change of distance.
Time is the duration between start and finish.

Question 25

How do distance v. time graphs work?

Answer 25

Refer to physical flashcard.