Define Newton's first law of motion .

A body will remain at rest or move with constant velocity unless acted on by a resultant force .

Define Newton's second law of motion .

The acceleration of an object with constant mass is directly proportional to the resultant force acting on it.

If the forces acting on an object are balanced, the .......... acting on it is zero.

If the forces acting on an object are balanced, the resultant force acting on it is zero.

Define terminal velocity .

The maximum, constant velocity reached when the drag forces become equal to the driving force, so the resultant force is zero and the object stops accelerating.

True or False? A skydiver reaches terminal velocity because their weight increases as they fall.

False. The skydiver's weight stays constant . As they accelerate, air resistance increases until it balances the weight, giving zero resultant force — this is what produces terminal velocity.

State two ways a designer could increase the maximum (terminal) velocity of a car.

increase the forward thrust by increasing the engine power reduce the opposing forces , e.g. by streamlining the body or reducing friction in the tyres, engine and bearings

The measure of the amount of matter in an object; it is the property that resists a change in motion . SI unit: kilogram (kg) .

At the Earth's surface the average .......... is 9.81 N kg -1 .

At the Earth's surface the average gravitational field strength is 9.81 N kg -1 .

Motion of a falling object where the only force acting is its weight — drag forces are ignored.

True or False? In freefall a heavier object accelerates faster towards the ground than a lighter one.

False. In freefall all objects fall with the same acceleration , regardless of their mass or weight, because the only force is weight.

What is the aim of Core Practical 1: Investigating the Acceleration of Freefall?

To determine a value for the acceleration due to gravity , g .

In the electromagnet method, residual .......... after the current is switched off may cause t to be recorded as longer than it should be.

In the electromagnet method, residual magnetism after the current is switched off may cause t to be recorded as longer than it should be.

State a key random error in the freefall drop experiments and how it is reduced.

The large uncertainty in h from a metre rule (1 mm precision) and parallax error when reading h . Reduced by repeating each height 3–5 times and averaging the time t .

State one safety precaution for the electromagnet freefall experiment.

Any one from: keep water away from the electromagnet and only switch on the current once set up, to avoid electrocution place a cushion to catch the ball bearing secure the tall clamp stand with a G-clamp

True or False? The ramp-and-trolley experiment shows that heavier objects roll down and accelerate faster than lighter ones.

False. This method is based on Galileo's inclined-ramp work, which showed that all objects accelerate at the same rate regardless of their weight .

Define Newton's third law of motion .

Whenever two bodies interact, the forces they exert on each other are equal in size , act in opposite directions , and are of the same type .

Newton's third-law force pairs always act on two different objects and are always of the .......... .

Newton's third-law force pairs always act on two different objects and are always of the same type .

How many objects do a Newton's third law force pair act on?

Two different objects — one force acts on each. If both forces act on a single object, it is Newton's first law, not the third law.

True or False? For a book resting on a table, its weight and the table's upward contact force on it form a Newton's third law pair.

False. Both forces act on a single object (the book) and are different types (gravitational and contact). This is a balanced-force situation described by Newton's first law.

Use Newton's third law to explain how a person is able to walk forwards.

The foot pushes the ground backwards ; by Newton's third law the ground pushes the foot forwards with an equal and opposite force, propelling the person forward.

If object A exerts a gravitational force on object B, what force does B exert on A?

B exerts an equal and opposite gravitational force on A — third-law pairs are always the same type of force.

Is momentum a scalar or a vector quantity, and why does this matter?

Momentum is a vector — it has both magnitude and direction. An object moving in the chosen positive direction has positive momentum; one moving the opposite way has negative momentum.

If an object travelling to the right has positive momentum, an object travelling to the left has .......... momentum.

If an object travelling to the right has positive momentum, an object travelling to the left has negative momentum.

Before calculating momentum, what unit conversions should you check?

convert mass in grams to kilograms (÷ 1000) convert velocity to m s -1 so the answer is in the SI unit kg m s -1 .

State the principle of conservation of linear momentum .

In a closed system , the total momentum before an event is equal to the total momentum after the event.

Momentum is always conserved in collisions where no .......... act.

Momentum is always conserved in collisions where no external forces act.

How can a system of moving objects have a total momentum of zero?

Because momentum is a vector , objects moving in opposite directions have opposite-sign momenta that can cancel, giving an overall momentum of zero.

In a 1D collision, how do you account for an object that rebounds backwards afterwards?

Assign it a negative velocity (and hence negative momentum), since momentum is a vector. Choose one direction as positive and keep the signs consistent throughout.

A LevelPhysicsEdexcelFlashcards2. MechanicsForces & Momentum

Forces & Momentum (Edexcel A Level Physics): Flashcards

Exam code: 9PH0

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FrontForce & Acceleration
Define Newton's first law of motion.

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Cards in this collection (40)

Define Newton's first law of motion.
A body will remain at rest or move with constant velocity unless acted on by a resultant force.
Define Newton's second law of motion.
The acceleration of an object with constant mass is directly proportional to the resultant force acting on it.
What equation expresses Newton's second law?
$Σ F = m a$
The symbol Σ signifies that F is the sum of the forces (the resultant force), not a single force acting alone.
If the forces acting on an object are balanced, the .......... acting on it is zero.
If the forces acting on an object are balanced, the resultant force acting on it is zero.
Define terminal velocity.
The maximum, constant velocity reached when the drag forces become equal to the driving force, so the resultant force is zero and the object stops accelerating.
True or False?
A skydiver reaches terminal velocity because their weight increases as they fall.
False.
The skydiver's weight stays constant. As they accelerate, air resistance increases until it balances the weight, giving zero resultant force — this is what produces terminal velocity.
State two ways a designer could increase the maximum (terminal) velocity of a car.
- increase the forward thrust by increasing the engine power
- reduce the opposing forces, e.g. by streamlining the body or reducing friction in the tyres, engine and bearings
Define mass.
The measure of the amount of matter in an object; it is the property that resists a change in motion. SI unit: kilogram (kg).
Define weight.
The force a body experiences due to being in a gravitational field, given by $W = m g$ where m is mass (kg) and g is gravitational field strength (N kg^-1).
What is the equation for gravitational field strength?
$g = \frac{F}{m}$
where F is weight (N) and m is mass (kg). Its unit is N kg^-1.
At the Earth's surface the average .......... is 9.81 N kg^-1.
At the Earth's surface the average gravitational field strength is 9.81 N kg^-1.
Explain the difference between mass and weight.
- mass is the amount of matter in an object, measured in kg, and is the same everywhere
- weight is the gravitational force on that mass, measured in N, and depends on the gravitational field strength ( $W = m g$ )
Define freefall.
Motion of a falling object where the only force acting is its weight — drag forces are ignored.
True or False?
In freefall a heavier object accelerates faster towards the ground than a lighter one.
False.
In freefall all objects fall with the same acceleration, regardless of their mass or weight, because the only force is weight.
What is the aim of Core Practical 1: Investigating the Acceleration of Freefall?
To determine a value for the acceleration due to gravity, g.
In the electromagnet-and-trapdoor drop method, what graph is plotted to find g, and how is g obtained?
Using $h = \frac{1}{2} g t^{2}$ , plot h (y-axis) against t² (x-axis). The straight line has gradient $\frac{1}{2} g$ , so g = 2 × gradient.
In the card-and-light-gate method, which SUVAT relationship is used and what is plotted?
Using $v^{2} = 2 g h$ , plot v² (y-axis) against 2h (x-axis). The straight line has gradient = g.
In the ramp-and-trolley method, what is plotted to find the acceleration?
Using $v = u + a t$ , plot velocity v (y-axis) against average time t (x-axis). The gradient gives the acceleration, which is provided by gravity.
In the electromagnet method, residual .......... after the current is switched off may cause t to be recorded as longer than it should be.
In the electromagnet method, residual magnetism after the current is switched off may cause t to be recorded as longer than it should be.
State a key random error in the freefall drop experiments and how it is reduced.
The large uncertainty in h from a metre rule (1 mm precision) and parallax error when reading h. Reduced by repeating each height 3–5 times and averaging the time t.
State one safety precaution for the electromagnet freefall experiment.
Any one from:
- keep water away from the electromagnet and only switch on the current once set up, to avoid electrocution
- place a cushion to catch the ball bearing
- secure the tall clamp stand with a G-clamp
True or False?
The ramp-and-trolley experiment shows that heavier objects roll down and accelerate faster than lighter ones.
False.
This method is based on Galileo's inclined-ramp work, which showed that all objects accelerate at the same rate regardless of their weight.
Define Newton's third law of motion.
Whenever two bodies interact, the forces they exert on each other are equal in size, act in opposite directions, and are of the same type.
Newton's third-law force pairs always act on two different objects and are always of the ...........
Newton's third-law force pairs always act on two different objects and are always of the same type.
How many objects do a Newton's third law force pair act on?
Two different objects — one force acts on each. If both forces act on a single object, it is Newton's first law, not the third law.
True or False?
For a book resting on a table, its weight and the table's upward contact force on it form a Newton's third law pair.
False.
Both forces act on a single object (the book) and are different types (gravitational and contact). This is a balanced-force situation described by Newton's first law.
Use Newton's third law to explain how a person is able to walk forwards.
The foot pushes the ground backwards; by Newton's third law the ground pushes the foot forwards with an equal and opposite force, propelling the person forward.
If object A exerts a gravitational force on object B, what force does B exert on A?
B exerts an equal and opposite gravitational force on A — third-law pairs are always the same type of force.
Define linear momentum.
The product of an object's mass and velocity: $p = m v$ .
What is the SI unit of momentum?
kg m s^-1
Is momentum a scalar or a vector quantity, and why does this matter?
Momentum is a vector — it has both magnitude and direction. An object moving in the chosen positive direction has positive momentum; one moving the opposite way has negative momentum.
If an object travelling to the right has positive momentum, an object travelling to the left has .......... momentum.
If an object travelling to the right has positive momentum, an object travelling to the left has negative momentum.
True or False?
A heavier object always has more momentum than a lighter one.
False.
Momentum depends on both mass and velocity ( $p = m v$ ). A light, fast object can have the same — or greater — momentum than a heavy, slow one.
Before calculating momentum, what unit conversions should you check?
- convert mass in grams to kilograms (÷ 1000)
- convert velocity to m s^-1
so the answer is in the SI unit kg m s^-1.
State the principle of conservation of linear momentum.
In a closed system, the total momentum before an event is equal to the total momentum after the event.
Momentum is always conserved in collisions where no .......... act.
Momentum is always conserved in collisions where no external forces act.
How can a system of moving objects have a total momentum of zero?
Because momentum is a vector, objects moving in opposite directions have opposite-sign momenta that can cancel, giving an overall momentum of zero.
In a 1D collision, how do you account for an object that rebounds backwards afterwards?
Assign it a negative velocity (and hence negative momentum), since momentum is a vector. Choose one direction as positive and keep the signs consistent throughout.
When trolley A collides with trolley B, how do the forces they exert on each other compare?
They are equal in magnitude and opposite in direction: $F_{B - A} = - F_{A - B}$ . So one trolley gains momentum while the other loses an equal amount.
True or False?
In a collision, two objects always experience equal-magnitude accelerations because the forces on them are equal.
False.
The forces are equal and opposite, but from $Σ F = m a$ the acceleration also depends on mass. Objects of unequal mass experience unequal accelerations.

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