SCNC1112 M0 L3

What object obeys the Newton’s Laws of motion?

all objects on Earth and in space

what is the difference between speed and velocity ?

speed is a scaler ( without direction )

velocity is a vector ( wit direction )

what is meant by acceleration in physics?

rate of change in velocity, not the increase i velocity.

Does a ciruclating object with constant speed has acceleration?

Yes, as the direction of motion keep changing, so the velocity is changing and there is acceleration

What does Galileo galilei discovered?

object fell with the same accelration regardless of mass

what is Newton;s first law

object remians at rest or moves in a st line at constant speed unless acted upon by an unbalanced force.
- Motion no need force to maintain
-Force is required to change the motion

-Circular motion requires a force because it is changing in direction.

What is Newton’s second Law?

F=ma

• For the same force, object with larger mass accelerates less

What is Newton’s Thrid Law?

Action and reaction pair

How to explain the motion of a ballon car using Newton’s Law?

1. releasing air posting a pushing force on air, while there is a reaction force acting on ballon by the air (3)

2. This force makes the ballon cart is experiencing an unbalanced force, so it accelerate from rest (1)

3. The extent it accelerates is inversely proportional to its mass (2)

What is Newton’s Law of universal gravitation

F=GMm/r²

The force governs the orbital motion of Earth and Moon is the same as why apple drops

how does the accelration due to gravity on Earth changes from distance?

on surface : 9.81 ( regardless the mass, their acceleration is the same )

further away from the Earth.
- As F=ma

• ma=GMm/r^r

• a=GM/r^r

• so the accelration is smaller when it is further away from the earth.

What is the different between mass and weight?

mass is the resistance ot change in motion, F=ma, larger mass, smaller its willingness to change in motion.

Weight is the force due to the gravity

what is the balance measuring?

The reactin force that equals to our weight

how does the reading of balance change in lift?

• accelerating upward: R-mg=ma, R=mg+ma, so the reading is higher

• decelerating upward; R-mg=-ma, R=mg-ma, so the reading is smaller

• Accelerating downward: R-mg=-ma, R=mg-ma, so the reading is smaller

• Decelerating downward: R-mg=ma, R=mg+ma, so the reading is higher

what is the unit of accelration?

ms^-2

what is the direction of the force?

parallel to the motion, acceleration

what is the unit of force?

N / kg ms^-2

what is meant by the F in F=ma?

Net force of an object
- If an object has unbalanced Net force, it will has accelration to change its motion

why the earth is not attracted to the apple?

Actually it is attracted, as there is a gravitational force between them. However, the mass of the earth is the large, so as its resistance of changing motion

Where is the gravitational force pointing at?

always at the centre of the plant

why we feel weightless when free falling in lift?

There is no supporting force

Is the mass and weight of hammer and feather the same on Earth and Moon?

mass; the same

weight, both are larger on Earth due to larger acceleration

Is that the falling time for hammer and feather the same on earth and Moon?

Moon: yes, due to the same accelration, and there is no friction, so same net force and same acceleration

earth: No, althgoh the accelration due the gravity is the same, there is air friction, so net force is different, and the acceleratin is different