3.2 Forces in action

Question 1

What is the unit of force?

Answer 1

Newton (N)

Question 2

True or false: Forces are vectors

Answer 2

True

Question 3

What is a Newton

Answer 3

1 N is the force required to accelerate a 1 kg object at 1 ms^-2

Question 4

How do you calculate weight?

Answer 4

W=mg

Question 5

What is the definition of tension?

Answer 5

Tension acts along a connector (i.e rope) being used to pull an object. It is the same size everywhere along the rope but changes direction if the rope changes direction (e.g going over a pulley).

Question 6

What is the definition of the normal contact force?

Answer 6

Force exerted by an object perpendicular to its surface when another object pushes on it.

Question 7

What is the definition of upthrust?

Answer 7

When an object displaces a fluid (liquid and gases), the fluid exerts a force upwards on the object.

Question 8

What is the definition of friction?

Answer 8

It’s a resistive force exerted by objects sliding. It acts in the opposite direction to the movement causing it.

Question 9

True or false: In a free body diagram the arrows go into the box ( which represents the object)

Answer 9

False, the arrows start from the inside heading outwards.

Question 10

True or false: drag is a frictional force?

Answer 10

True

Question 11

When is drag experienced?

Answer 11

When travelling through a fluid.

Question 12

List 4 factors that increase the drag force:

Answer 12

• Increased surface area
• Increased speed
• the fluid is more viscous
• the objects shape is less aerodynamic

Question 13

List 2 factors that increase the size of the drag force:

Answer 13

• Increased surface area
• Increased speed
• the fluid is more viscous
• the objects shape is less aerodynamic

Question 14

When does terminal velocity occur?

Answer 14

When a object is in free fall, and the drag force is equal to the weight. Therefore there is no resultant force.

Question 15

What happens at terminal velocity?

Answer 15

W=D, acceleration=0

Question 16

What is a moment?

Answer 16

The turning effect of a force

Question 17

what is the relationship between distance, moments and force?

Answer 17

Moment = Fx

Question 18

True or false: moments are scalar.

Answer 18

False they are vectors

Question 19

what is a couple?

Answer 19

Pair of forces that together cause a resultant moment but not a resultant force. The forces have to be the same size acting in opposite directions.

Question 20

What is a torque?

Answer 20

The resultant moment.

Question 21

How do you calculate the torque due to a couple?

Answer 21

Torque = F d

Question 22

What is the principle of moments?

Answer 22

For an object to be in equilibrium the sum of the clockwise moments must equal the sum of the anticlockwise moments exerted on it.

Question 23

What is the centre of gravity?

Answer 23

A point where it appears the objects weight acts.

Question 24

What is the centre of mass?

Answer 24

The average position of the objects mass. The same as the centre of gravity if in a uniform field.

Question 25

How to determine the centre of gravity of a flat shape?

Answer 25

- Suspend the shape - Suspend a plumb line and mark the position at rest - repeat for other positions with the pin - The centre of g is where the lines cross.

Question 26

When is an object in equilibrium?

Answer 26

- net force = 0 - net moment = 0

Question 27

What is density?

Answer 27

mass per unit volume

Question 28

What is pressure?

Answer 28

pressure exerted by a force on an area.

Question 29

What is the equation for pressure in a liquid?

Answer 29

P=hpg

Question 30

What does Archimedes principle state?

Answer 30

The upthrust exerted by a fluid is equal to the weight of the displaced fluid.

Question 31

How to calculate upthrust?

Answer 31

U= density(p)volume(V)gravity(g)

Question 32

True or false: an object will sink if it is less dense than the fluid.

Answer 32

False,it will float

Question 33

When is the resultant force of an object in fluid 0?

Answer 33

When it's floating. Upthrust = Weight

Question 34

What is the ratio which shows the fraction of the height of an object submerged?

Answer 34

po/pf=d/h. where po is equal to the density of the object, pf is the density of the fluid. h is height and d is depth when floating.

Question 35

What is the ratio which shows the fraction of the volume submerged?

Answer 35

po/pf. po=density of object, pf=density of fluid.