0.4 Mechanics

Question 1

What is a scalar?

Answer 1

A quantity that only has amount (magnitude).

Question 2

What is a vector?

Answer 2

A quantity with both direction and magnitude.

Question 3

Name 6 scalars.

Answer 3

1) Time
2) Mass
3) Temperature
4) Length
5) Speed
6) Energy

Question 4

Name 6 vectors.

Answer 4

1) Weight
2) Acceleration
3) Force
4) Displacement
5) Velocity
6) Momentum

Question 5

What are two different ways to combine vectors?

Answer 5

• Drawing scale diagrams
• Using pythagoras and triganometry

Question 6

When answering questions about vectors, if the vector given uses directions of a compass, then you should what?

Answer 6

Then your answer must be given as a bearing.

Question 7

How do you show forces acting on an object?

Answer 7

Drawing a free body diagram.

Question 8

What does it mean for an object to be in equilibrium?

Answer 8

When all forces acting on the object are balanced and cancel each other out.
- This also includes rotational forces (moments)
- The resultant force will therefore be 0 aswell as acceleration.

Question 9

What is the official definition of a moment?

Answer 9

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

Question 10

What is the equation for a moment?

Answer 10

M = F x d
Moment = force x perpendicular distance from pivot to the line of action of force

Question 11

What is the Principle of moment?

Answer 11

If a system is in equilibrium,
the sum of the clockwise moments = the sum of the anticlockwise moments

Question 12

What is a couple?

Answer 12

A pair of forces that are equal in size and act parallel to each other but in opposite direction.

Question 13

What is the centre of mass?

Answer 13

The single point where all the weight is considered to act through.

Question 14

What does uniform mean?

Answer 14

The density of the material is the same throughout, resulting in the centre of mass always being in the middle.

Question 15

What is the definition of displacement?

Answer 15

Distance and direction from the starting point in a straight line.

Question 16

What is the definition of speed?

Answer 16

How fast something is going regardless of direction.

Question 17

What is the definition of velocity?

Answer 17

How fast something is going with direction.

Question 18

What is the definition of acceleration?

Answer 18

The rate of change of velocity.

Question 19

If a object is not accelerating, what formulae can we use?

Answer 19

Speed = Distance / Time

Question 20

However if an object is accelerating, what equations can we use?

Answer 20

SUVAT equations

Question 21

What does the gradient of a displacement time graph represent?

Answer 21

Velocity

Question 22

What does a curved line represent in a displacement time graph?

Answer 22

Changing velocity / acceleration

Question 23

What does the gradient of a velocity time graph represent?

Answer 23

Acceleration

Question 24

What does the area under the line represent in a velocity time graph?

Answer 24

Displacement

Question 25

What are the two methods to work out the area under the graph?

Answer 25

1) Divide up into triangles and rectangles (for a straight line) 2) Count the squares (use for curved lines)

Question 26

What does a curved line on a velocity time graph show?

Answer 26

A change of acceleration

Question 27

What does the area under the line of an acceleration time graph represent?

Answer 27

Change in velocity

Question 28

What does Newtons 1st Law state?

Answer 28

If there are no resultant forces acting on an object it will either: 1) Stay at rest 2) Travel at a constant speed in a straight line

Question 29

What does Newtons 2nd Law state?

Answer 29

The acceleration of an object is proportional to the resultant force acting on it: F = m x a - Where there is an acceleration ther must be a force - Where there is a force there is an accereleration

Question 30

What does Newtons 3rd Law state?

Answer 30

If object A exerts a force on object B, then object B exercts an equal but opposite force on object A

Question 31

What are the rules for Newtons 3rd Law?

Answer 31

1) Two objects involved 2) Same type of force 3) Same size but in opposite directions

Question 32

What does freefall mean?

Answer 32

When an object is in freeall the only force acting on that object is its weight.

Question 33

What is air resistance proportional to?

Answer 33

Surface area and speed

Question 34

Why when there is no acceleration do all objects accelerate at the same rate?

Answer 34

Because acceleration is independent of mass.

Question 35

How did Galileo record freefall 'accurately'?

Answer 35

He rolled balls with different masses down a slope. - Acceleration is still caused by gravity but rolled slower, making it easier to time and for air resistance to be negligible. - He timed how long it took the balls to roll down different lengths of the slope and found the distance travelled was always the same.

Question 36

What is a projectile?

Answer 36

An object where the only force acting on it is it's weight, therefore it is in freefall.

Question 37

Is there a horizontal force acting on a projectile?

Answer 37

No, as we are assuming that air resistance is negligible.

Question 38

If there is no horizontal force acting on a projectile, then what happens to the horizontal velocity?

Answer 38

It will stay constant.

Question 39

How do you calculate the horizontal component (projectiles)?

Answer 39

Horizontal component = horizontal velocity x time in air

Question 40

Why will the projectile accelerate in the vertical direction?

Answer 40

Because the vertical force of weight is acting on it, and acceleration is typically due to g=9.81m/s^2

Question 41

If the projectile is fired horizontally then what is the vertical speed be?

Answer 41

Speed will be 0

Question 42

For every second a projectile is in flight how much velocity will be gained?

Answer 42

9.81 ms^-1

Question 43

Is the vertical and horizontal components of motion related?

Answer 43

No they are completely independent.

Question 44

What difference will air resistance will air resistance make to a projectiles path if it is no negligible?

Answer 44

- The horizontal velocity will slowly decrease to 0 as a horizontal force is now acting. - It will therefore not travel as far horizontally. - The projectile will gain vertical speed more slowly.

Question 45

What is the simple definition on for friction?

Answer 45

- It is a force that opposes motion - It turns kinetic energy into thermal energy - It can never speed things up or start them moving.

Question 46

What are the two types of friction?

Answer 46

1) contact friction 2) fluid friction

Question 47

What is contact friction?

Answer 47

Friction between two solid surfaces.

Question 48

What is fluid friciton?

Answer 48

Better known as drag, which is caused by a gas or a liquid.

Question 49

What does drag increase with?

Answer 49

- Larger surface area (of the projectile) - Larger speed (proportional to speed squared) - Larger density (viscosity) of fluid - Nothing to do with mass

Question 50

What is lift?

Answer 50

Lift is an upwards force on an object moving through a fluid. It happens when the shape of an object causes the fluid flowing over it to change direction.

Question 51

What direction does lift act?

Answer 51

Perpendicular to the direction of fluid flow (relative to the object)

Question 52

What direction does drag act?

Answer 52

Drag acts parallel to the direction of the fluid flow.

Question 53

What is terminal velocity?

Answer 53

The maximum speed of an object that occurs when the resistive and driving forces acting on the object are equal to each other.

Question 54

What is linear momentum?

Answer 54

The product of an objects mass and velocity. It is a vector quantitiy.

Question 55

What is the equation of momentum?

Answer 55

Momenmtum = mass x velocity

Question 56

What does the principle of (conservation of) linear momnetum state?

Answer 56

The momentum before collision = total momentum after collision, provided no external forces act.

Question 57

What does inelastic collision mean?

Answer 57

- Momentum conserved - Kinetic energy NOT conserved - Most collisions in real life are inelastic - Energy is lost as heat and sound

Question 58

What does elastic collisions mean?

Answer 58

- Momentum conserved - Kinetic energy conserved

Question 59

What happens in an elastic collision between two objects of the same mass?