Vertical and Horizontal Forces

Question 1

Definition of weight

Answer 1

The gravitational pull that the earth exerts on a body

Question 2

Where does weight act?

Answer 2

Downwards from a body centre of mass

Question 3

What is the equation to calculate weight?

Answer 3

Weight = mass x acceleration due to gravity

Question 4

What are the units of weight?

Answer 4

Newtons

Question 5

What is acceleration due to gravity measured in?

Answer 5

m/s/s

Question 6

Definition of reaction

Answer 6

The equal and opposite force exerted by a body in response to the action force placed upon it

Question 7

What is reaction measured in?

Answer 7

Newtons

Question 8

What is reaction a result of?

Answer 8

Newtons 3rd law

Question 9

How can reaction been shown?

Answer 9

Vertical arrow extending upwards from the point of contact with the surface

Question 10

What are the two vertical forces?

Answer 10

Weight, Reaction

Question 11

What are the two horizontal forces?

Answer 11

Friction, Air resistance

Question 12

Definition of friction

Answer 12

The force that opposes the motion of two surfaces in contact

Question 13

What is friction measured in?

Answer 13

Newtons (N)

Question 14

How can friction be shown on a diagram

Answer 14

Horizontal arrow extending (usually) in the direction as motion from the point of contact parallel to the sliding surface

Question 15

What are the factors affecting friction?

Answer 15

1. Roughness of the ground surface
2. Roughness of the contact surface
3. Temperature
4. Size of normal reaction

Question 16

Explain with sporting examples the 5 factors affecting friction?

Answer 16

1. Roughness of the ground surface - by increasing the roughness of ground surface, friction is increased
   eg. athletes run on rubberised tracks
2. Roughness of the contact surface - by increasing roughness of contact surface, friction is increased
   eg. sprinters, jumpers wear spikes shows
3. Temperature - increasing the temperature of the ground and contact surface, friction is increased
   eg. F1 drivers have a ‘warm-up’ lap on the track
4. Size of normal reaction - by increasing normal reaction, friction is increased
   eg. shot putters have a high mass and due to Newtons 3rd law this creates an equal and opposite high reaction force

Question 17

Definition of air resistance

Answer 17

The force that opposes the motion of a body travelling through the air

Question 18

What is air resistance measured in?

Answer 18

Newtons (N)

Question 19

How is air resistance shown on a diagram?

Answer 19

A horizontal arrow extending against the direction of motion from the centre of mass

Question 20

What are the factors affecting air resistance?

Answer 20

1. Velocity
2. Shape
3. Frontal cross-sectional area
4. Smoothness of surface

Question 21

Explain with sporting examples that factors that affect air resistance?

Answer 21

1. Velocity - by increasing velocity, air resistance increases
   eg. the greater the velocity of a sprint cyclist around the velodrome track, the greater the force of air resistance opposing there motion
2. Shape - the more aerodynamic the shape the lower the air resistance
   eg. the shape of a cyclists helmet, streamlining to create a smooth air flow around an aerodynamic shape
3. Frontal cross-sectional area - by decreasing the frontal cross-sectional area, air resistance decreases
   eg. low, crouched position of giant slalom skiers in straights
4. Smoothness of surface - by increasing the smoothness of a surface, air resistance decreases
   eg. smooth lycra suits of sprinters, cyclists, skiers

Question 22

How else can air resistance be decreased within cycling?

Answer 22

Drafting, cyclists take turns at the front of the pack putting their frontal cross-sectional area to the oncoming body of air. Cyclists behind will sit in their slip stream, sheltered to oncoming air and use roughly 33% less energy

Question 24

What do free body diagrams show?

Answer 24

All the forces acting on a body at a particular instant in time

Question 25

What is the origin and direction of weight in a free body diagram?

Answer 25

From the centre of mass extending vertically downwards

Question 26

What is the origin and direction of reaction in a free body diagram?

Answer 26

From the point of contact extending vertically upwards

Question 27

What is the relationship between weight and reaction?

Answer 27

-W=R, net force is zero, all the forces are balanced, the body will remain at rest or constant vertical velocity -R>W, the net force is positive, forces are unbalanced and acceleration will occur in an upward direction

Question 28

What is the origin and direction of friction in a free body diagram?

Answer 28

From the point of contact and usually extending horizontally in the same direction as motion (parallel to the surface)

Question 29

What is the origin and direction of air resistance in a free body diagram?

Answer 29

From the centre of mass and extending horizontally against the direction of motion

Question 30

What is the relationship between friction and air resistance?

Answer 30

-F=AR, net force is zero, all forces are balanced, body will continue to travel in a constant velocity -F>AR, net force is positive, forces are unbalanced, acceleration in the forwards direction -F