P2.3 Forces in Action

Question 1

What is a force?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

What is meant by inelastic deformation?

Answer 3

• A deformation which results in the object being permenantly deformed
• The object doesn’t return to its original shape when the force is removed

Question 4

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

Answer 4

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

Question 5

What is hooke’s law?

Answer 5

Hooke’s law states that the force applied is directly proportional to the extension of an elastic object.

Question 6

At what point does Hooke’s Law no longer apply?

Answer 6

The Limit of Proportionality

Question 7

What does the limit of proportionality look like on an extension-load graph?

Answer 7

Where the graph stop being linear

Question 8

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

Answer 8

Elastic Potential Energy

Question 9

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

Answer 9

Compression

Question 10

What is the equation for elastic potential energy? Give SI units for all quantities involved.

Answer 10

E = 1/2 k x^2

Question 11

What is weight?

Answer 11

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

Question 12

What quantities does weight depend on?

Answer 12

• 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

Newtons (N)

Question 14

What is the unit for gravitational field strength?

Answer 14

N/kg

Question 15

What is the equation used to calculate weight?

Answer 15

Weight (N) = mass (kg) x gravitational field strength (N/kg)

Question 16

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

Answer 16

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

Question 17

What type of field does all matter have?

Answer 17

A gravitational field

Question 18

How does the gravitational field of an object change as the object becomes more massive?

Answer 18

The field strength increases

Question 19

What letter is used to represent gravitational field strength and what is its value at the surface of Earth?

Answer 19

• g

- The value of g on the surface of the Earth is approximately 10N/kg

Question 20

What is the acceleration of an object falling in free fall with no resistive forces acting?

Answer 20

10m/s^2

Question 21

Why would your weight be different if you were on a different planet?

Answer 21

Different gravitational field strength, weight is a product of mass and gravitational field strength

Question 22

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

Answer 22

A calibrated spring-balance or newton-meter

Question 23

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

Answer 23

A moment

Question 24

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

Answer 24

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

Question 25

What distance measurement is used when calculating a moment?

Answer 25

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

Question 26

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

Answer 26

The clockwise moments are equal to the anticlockwise moments.

Question 27

What does the direction of a resultant moment acting on an object tell you?

Answer 27

The direction that the object will rotate around the pivot point.

Question 28

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

Answer 28

At right angles (normal to) the surface.

Question 29

What can be said about the pressure in a simple hydraulic system?

Answer 29

The pressure in the fluid is constant through the fluid (it cannot be compressed or expanded)

Question 30

Explain how a simple hydraulic lift works.

Answer 30

• The pressure is constant in the fluid
• Force applied on each platform is equal to the product of pressure and area
  (F = pA)
• One platform has a larger area than the other meaning the force produced is
  greater than the force applied to the smaller platform