Newtons Law of Motion

Motion

What is Newton’s first law of motion?

An object will remain at rest or continue moving at constant velocity unless acted on by a resultant force.

What happens to a stationary object if there is no resultant force?

It remains stationary.

What happens to a moving object if there is no resultant force?

It continues moving at the same speed in the same direction.

What does constant velocity mean?

Moving at a constant speed in a constant direction.

What is the resultant force on an object moving at constant velocity?

Zero.

What resultant force is needed to change an object's motion?

A non-zero resultant force.

What can a resultant force change?

The speed, direction, or both the speed and direction of an object.

What is Newton’s second law of motion?

The acceleration of an object is proportional to the resultant force and inversely proportional to its mass.

What is the equation for Newton’s second law?

ΣF = ma.

What does ΣF represent in ΣF = ma?

The resultant force acting on the object, measured in newtons (N).

What does m represent in ΣF = ma?

The mass of the object, measured in kilograms (kg).

What does a represent in ΣF = ma?

The acceleration of the object, measured in m s⁻².

How do you calculate resultant force using Newton’s second law?

Resultant force = mass × acceleration.

How do you calculate acceleration using Newton’s second law?

a = F/m.

How do you calculate mass using Newton’s second law?

m = F/a.

What is the SI unit of force?

The newton (N).

What is one newton?

The force required to accelerate a mass of 1 kg at 1 m s⁻².

What happens to acceleration if resultant force increases while mass stays constant?

Acceleration increases in direct proportion to the resultant force.

What is the relationship between acceleration and resultant force for constant mass?

a ∝ F.

What graph demonstrates that acceleration is directly proportional to force?

A graph of acceleration against force gives a straight line through the origin.

What happens to acceleration if mass increases while resultant force stays constant?

Acceleration decreases.

What is the relationship between acceleration and mass for constant resultant force?

Acceleration is inversely proportional to mass.

What is the relationship between acceleration and 1/mass?

Acceleration is directly proportional to 1/mass.

What graph demonstrates that acceleration is inversely proportional to mass?

A graph of acceleration against 1/mass gives a straight line through the origin.

Why does a larger mass have a smaller acceleration for the same force?

From a = F/m, increasing the mass reduces the acceleration.

What is a control variable?

A quantity that is kept constant during an experiment.

In an experiment investigating acceleration and force, what should be kept constant?

The total mass.

In an experiment investigating acceleration and mass, what should be kept constant?

The resultant force.

What does a straight-line graph show?

A linear relationship between the variables.

What is the general equation of a straight line?

y = mx + c.

What does m represent in y = mx + c?

The gradient of the line.

What does c represent in y = mx + c?

The y-intercept.

When are two quantities directly proportional?

When their graph is a straight line that passes through the origin.

What does a straight line through the origin mean?

One quantity is directly proportional to the other.

How can gravitational acceleration be calculated using Newton’s second law?

g = F/m, where F is the gravitational force acting on the mass.

What equation links weight, mass and gravitational field strength?

W = mg.

What is Newton’s third law of motion?

When object A exerts a force on object B, object B exerts an equal and opposite force on object A.

What is the simple statement of Newton’s third law?

For every action, there is an equal and opposite reaction.

What are Newton’s third-law force pairs?

Two equal and opposite forces produced by the interaction of two objects.

What is the magnitude of the two forces in a Newton’s third-law pair?

They are equal in magnitude.

What are the directions of forces in a Newton’s third-law pair?

They act in opposite directions.

Do Newton’s third-law forces act on the same object?

No. They act on different objects.

Why do Newton’s third-law forces not cancel each other out?

They act on different objects.

When a footballer kicks a ball, what is the Newton’s third-law pair?

The foot exerts a force on the ball and the ball exerts an equal and opposite force on the foot.

When a person pushes against a wall, what is the Newton’s third-law pair?

The person pushes on the wall and the wall pushes back on the person with an equal and opposite force.

Why might a wall not noticeably accelerate when a person pushes it?

The wall is connected to the Earth, giving the system an extremely large mass and therefore a tiny acceleration.

How does Newton’s second law explain why a large mass has a small acceleration?

For the same force, a = F/m, so a larger mass produces a smaller acceleration.

What is the difference between balanced forces and a Newton’s third-law pair?

Balanced forces act on the same object and give zero resultant force, while third-law forces act on different objects.

Why does a book remain stationary on a table?

Its weight downward is balanced by the normal contact force from the table upward, so the resultant force is zero.

What happens if an upward force on a book becomes greater than its weight?

There is an upward resultant force, so the book accelerates upwards.

If the resultant force on an object is zero, what is its acceleration?

Zero.

If an object's acceleration is zero, what can you say about its velocity?

Its velocity is constant, which can include being stationary.

If the same resultant force acts on two objects of different masses, which accelerates more?

The object with the smaller mass.

If the same mass experiences a larger resultant force, what happens to its acceleration?

Its acceleration increases.

A 2 kg object experiences a resultant force of 10 N. What is its acceleration?

5 m s⁻².

A 5 kg object accelerates at 3 m s⁻². What is the resultant force?

15 N.

A 20 N resultant force produces an acceleration of 4 m s⁻². What is the object's mass?

5 kg.