4.10 - Newtons 1st & 2nd Laws

Question 1

What does Newton’s First Law state first an object travelling in a straight line?

Answer 1

If the resultant force on a moving object is zero, it will just carry on moving at a constant speed in a straight line.

Question 2

What does Newton’s First Law state for stationary objects?

Answer 2

If the resultant force on a stationary object is zero, the object will remain stationary.

Question 3

What happens if a non-zero force acts at 90 degrees to an object’s direction of motion?

Answer 3

The object will travel in a circle at a constant speed

Question 4

Objects in a circular motion (4)

Answer 4

• If an object is travelling in a circle it’s constantly changing direction. This means that a resultant force is acting on the object.
• This force always acts towards the centre of the circle and is always perpendicular to the line of motion of the object.
• So the object never changes speed because the force doesn’t act in the same or opposite direction to the object’s motion.
• However, the velocity of the object is constantly changing, as its direction is constantly changing and velocity is a vector.

Question 5

What is Newton’s Second Law?

Answer 5

• When a resultant force acts on an object, it causes a change in the object’s velocity. As momentum = mass x velocity, this means that the resultant force also causes a change of momentum in the direction of the force.
• Newton’s second law says that this change of momentum is proportional to the size of the resultant force and the time over which the force acts on the object.

Question 6

Why do we still say the moon is accelerating while it is orbiting the moon when the speed remains the same?

Answer 6

The direction is always changing slightly. This happens because the earth’s mass exerts a gravitational pull on the moon, which acts perpendicular to the moon’s motion. Overall, the moon orbits the earth with a constantly changing velocity (because the direction is changing) but a constant speed.

Question 7

What is inertia?

Answer 7

The tendency for the motion of an object to remain unchanged. Unless acted on by a resultant force, objects at rest will stay at rest and objects in motion will stay in motion.

Question 8

What is an object’s inertial mass?

Answer 8

How difficult it is to change an object’s velocity

Question 9

What is the equation to find an object’s inertial mass?

Answer 9

Force/acceleration

Question 10

A _____________ force is required to change the motion of an object

Answer 10

resultant

Question 11

A moving object that has no resultant force acting upon it will:

Answer 11

Continue moving at the same velocity

Question 12

The formula for Newton’s Second Law is:

Answer 12

F = ma