Types Of Forces

Front 1

Sliding Friction

Back 1

The force that exists between two adjacent surfaces which are in relative motion. It is usually slightly less than the limiting frictional force between the surfaces.

Front 2

Laws of friction

Back 2

1) The frictional force between two surfaces opposes their relative motion or attempted motion.

2) Frictional Forces are independent of the area of contact of the surfaces.

3) For two surfaces which have no relative motion the limiting frictional force is directly proportional to the normal reaction.

Front 3

Tension

Back 3

The force that is transmitted through a string, rope, cable or wire when it is pulled tight by forces acting from opposite ends. Tension is directed along the length of the wire and pulls equally on the object on the opposite ends of the wire.

Front 4

Newton's Law of Universal Gravition

Back 4

Every particle in the universe attracts every other with a force which is proportional to the product of their masses and inversely proportional to the square of their separation.

Front 5

Conditions for Newton's law of universal gravitation

Back 5

i) Valid for 2 bodies regardless of the sizes as long as they possess spherical symmetry.

ii) A good approximation when 1 body possesses spherical symmetry and the other is small in comparison to the separation of their centers.

iii) A good approximation when neither bodies possesses spherical symmetry but are both small in comparison to the separation of their center.

Front 6

Moment of a force (Equ)

Back 6

T = Fd measured in Nm

Front 7

Couples

Back 7

Two forces which are equal in magnitude and anti-parallel.

1: There is no direction in which a couple can give rise to a resultant force and thus a couple can produce a turning effect only - it cannot produce translation motion.

2: Since a single force is bound to produce translation, it follows that a couple cannot be represented by a single force.

Front 8

For a body at rest, it is in equilibrium if

Back 8

A) The acceleration of its center of mass is zero in all directions.

B) Its angular acceleration is zero.

Front 9

For a body in motion, it is in equilibrium if

Back 9

A) The resultant force on its center of mass is zero

B) The total torque about all axes is zero.

Front 10

To show that coplanar forces are in equilibrium, then

Back 10

1) The resultant force in any 2 directions in the plane of the forces is zero.

2) The total torque about any one axis which is perpendicular to the plane of the forces is zero.

Front 11

If a body is in equilibrium:

Back 11

1) The resultant force is zero in all directions

2) The total torque is zero about any axis.

Front 12

Pressure

Back 12

Force per unit area that acts perpendicular to the surface.

Refer to handout for units.

Front 13

Pressure on an object immersed in fluid

Back 13

1) Pressure within a fluid increases with depth. All points at the same depth within a fluid are at the same pressure.

2) Any surface in a fluid experiences a force as a result of the pressure within the fluid:

i) regardless of the orientation of the surface, the force is exerted perpendicular to the surface.

ii) The magnitude of the force exerted is independent of the orientation of the surface.

Front 14

Stokes' Law

Back 14

Consider a sphere of radius r that moves with velocity v, through a fluid with coefficient of viscosity n. A viscous force F is exerted on the sphere and the direction of this force opposes the movement of the sphere.

Front 15

Stokes' law applications

Back 15

1) Applies strictly to a fluid of infinite extent

2) Does not hold if the sphere is moving so fast resulting in non-streamline conditions.

Front 16

Terminal Velocity

Back 16

If there is no longer a net force acting on an object, the velocity has a constant maximum value known as its terminal velocity Vt.