Forces and energy

What are the types of forces?

non-contact force and contact force.

What is a contact force?

A force acting between two objects is in physical contact with each other.

What is the SI unit of force?

N (newtons)

What is a vector quantity?

A number quantity that has a MAGNITUDE, UNIT and DIRECTION.

LIKE,

Time,

Mass,

Volume,

Temperature,

Angle,

Distance,

Speed,

Light,

Intensity,

Loudness,

Energy,

Density

What is a scalar quantity?

A numerical quantity that has a MAGNITUDE and a UNIT. (but no directions)

Velocity,

Acceleration,

Displacement,

Force,

Weight (as weight is a force)

When the net force is zero, what is happening? (two situations)

The object is either NOT MOVING (STATIONARY, it is the better term), or it is moving at a constant velocity.

Forces should be drawn at? How is the CG found? (in uniformed objects). What is an exception?

THE CG. The CG is in the middle of an object. Use dotted lines to find it (not circles)

BUT, the frictional force is drawn at the area where the object meets a surface. (also it opposes motion)

(BTW, CG will divert towards a part of an object which is heavier)

Changes of gravitational field strength. (what changes it?)

The distance between the centre of a planet.

CLOSER TO CENTER OF EARTH (e.g, STRONGER GRAVITATIONAL FIELD STRENGTH.

FARTHER FROM THE CENTRE OF EARTH (e.g, WEAKER GRAVITATIONAL FIELD STRENGTH.

What is the effect of forces?

Move a stationary object

Change the speed of an object

Change the direction of an object

Stop a moving object

Change the shape or size of an object

What is pressure?

The amount of force acting on a specific area.

FORMULA=

P=N/SA (force/surface area)

Pressure is affected by?

Temperature

Force

Surface area

An example is in the sea. Deeper into the sea, more water is pushing onto you. This leads to an increase in force (increase of the weight of water pushing onto you), and this increases pressure.

Difference in pressure (example, suction cups)

I cant explain this well. But in terms of the suction cups,

• You push the air out of the gap between the suction cup and the surface.

• This creates a low-pressure area inside the suction cup because there’s less air trapped.

• Meanwhile, the atmospheric pressure outside the suction cup remains higher.

• Since atmospheric pressure is greater than the pressure inside, it pushes the suction cup firmly against the surface.

• This pressure difference holds the suction cup in place.