New
New
Year 11
•
OCR
•
Higher
Newton's Second Law (including inertia)
I can explain what the equation F = m × a means and use it to carry out calculations.
New
New
Year 11
•
OCR
•
Higher
Newton's Second Law (including inertia)
I can explain what the equation F = m × a means and use it to carry out calculations.
Lesson details
Key learning points
- Resultant force = mass × acceleration, F = m × a.
- An object that is thrown in the air experiences a constant gravitational force towards the centre of the Earth.
- An object that is thrown in the air is constantly accelerating towards the centre of the Earth.
- Inertial mass is a measure of how hard it is to change the velocity of an object.
- Inertial mass = force ÷ acceleration, m = F ÷ a.
Common misconception
When applying the equation F = m × a, pupils may take F to be any one of the forces acting on the object, rather than specifically the resultant force.
Provide some more complex examples, in which forces act in opposite directions, so pupils are required to work out the resultant force in preparation for completing calculations.
Keywords
Resultant force - The overall effect of the forces acting on an object.
Acceleration - Caused by a resultant force and results in a change in speed and/or direction of movement.
Mass - The amount of matter in an object, measured in kilograms (kg).
Inertial mass - The mass determined by Newton’s Second Law of Motion; m = F ÷ a.
For some classes, it may be appropriate to rearrange equations before substituting numbers, which prepares pupils for solving complex calculations more effectively in A–level physics.
Teacher tip
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Video
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Starter quiz
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6 Questions
Q1.
Match the following quantities to the correct unit.
Correct Answer:mass,kilograms
mass -
kilograms
Correct Answer:displacement,metres
displacement -
metres
Correct Answer:velocity,metres per second
velocity -
metres per second
Correct Answer:acceleration,metres per second squared
acceleration -
metres per second squared
Correct Answer:force,newtons
force -
newtons
Q2.
Which of the following statements about the acceleration of an object are correct?
Correct answer: The greater the resultant force, the greater the acceleration of an object.
The greater the resultant force, the greater the acceleration of an object.
The greater the resultant force, the lower the acceleration of an object.
The greater the mass, the greater the acceleration of an object.
Correct answer: The greater the mass, the lower the acceleration of an object.
The greater the mass, the lower the acceleration of an object.
Acceleration is independent of mass.
Q3.
Which single word is used to describe slowing down due to a resultant force?
Correct Answer: deceleration, decelerate
deceleration, decelerate
Q4.
A resultant force of 20 N is used to accelerate each of the following objects.
Which of the objects will be travelling fastest after 5 seconds?
Correct answer: A ball of mass 0.5 kg.
A ball of mass 0.5 kg.
A brick of mass 1.0 kg.
A bicycle and rider of mass 80 kg.
A motorcycle and rider of mass 150 kg.
A car of mass 900 kg.
Q5.
A blue and green snooker ball, of equal mass, have resultant forces acting them for 0.1 s; 20 N on the blue ball and 40 N on the green ball.
Which of the following statements are correct?
The balls will have equal acceleration.
Correct answer: The green ball accelerates at a greater rate than the blue ball.
The green ball accelerates at a greater rate than the blue ball.
The balls will be moving at the same speed after 0.1 s.
The blue ball will be moving faster after 0.1 s.
Correct answer: The green ball will be moving faster after 0.1s
The green ball will be moving faster after 0.1s
Q6.
A pupil investigates how mass affects the acceleration of a trolley using hanging masses to produce a force.
What should they do with a mass when they remove it from the mass holder?
Place it safely on the desk.
Correct answer: Place it on top of the trolley to keep the test fair.
Place it on top of the trolley to keep the test fair.
It does not matter where the mass is placed.
Place it back on the mass holder to keep the test fair.
Remove an equal mass from the top of the trolley.
Exit quiz
Download exit quiz
6 Questions
Q1.
Match the following key words and phrases to their explanations.
Correct Answer:resultant force,The overall effect of the forces acting on an object.
resultant force -
The overall effect of the forces acting on an object.
Correct Answer:acceleration,A change in velocity caused by a resultant force.
acceleration -
A change in velocity caused by a resultant force.
Correct Answer:inertial mass,The mass of an object based on how it accelerates when a force acts.
inertial mass -
The mass of an object based on how it accelerates when a force acts.
Q2.
Which of following is a statement of Newton’s Second Law of motion?
speed = distance ÷ time
acceleration = change in velocity ÷ time taken
mass = force × acceleration
acceleration = force × mass
Correct answer: force = mass × acceleration
force = mass × acceleration
Q3.
Starting with the smallest force, sort the following into order of increasing resultant force acting on the objects.
1 - A firework rocket of mass 0.20 kg accelerating at 20 m/s$$^2$$.
1
- A firework rocket of mass 0.20 kg accelerating at 20 m/s$$^2$$.
2 - A bicycle of mass 60 kg accelerating at 3.0 m/s$$^2$$.
2
- A bicycle of mass 60 kg accelerating at 3.0 m/s$$^2$$.
3 - A van of mass 1500 kg accelerating at 0.5 m/s$$^2$$.
3
- A van of mass 1500 kg accelerating at 0.5 m/s$$^2$$.
4 - A motorcycle of mass 200 kg accelerating at 4.0 m/s$$^2$$.
4
- A motorcycle of mass 200 kg accelerating at 4.0 m/s$$^2$$.
5 - A car of mass 900 kg accelerating at 1.5 m/s$$^2$$.
5
- A car of mass 900 kg accelerating at 1.5 m/s$$^2$$.
Q4.
Which of following objects have an inertial mass of 1 kg?
One that accelerates at 4 m/² when a resultant force of 2 N is acting.
Correct answer: One that accelerates at 2 m/s² when a resultant force of 2 N is acting.
One that accelerates at 2 m/s² when a resultant force of 2 N is acting.
One that accelerates at 2 m/s² when a resultant force of 4 N is acting.
Correct answer: One that accelerates at 4 m/s² when a resultant force of 4 N is acting.
One that accelerates at 4 m/s² when a resultant force of 4 N is acting.
Correct answer: One that accelerates at 0.5 m/s² when a resultant force of 0.5 N is acting.
One that accelerates at 0.5 m/s² when a resultant force of 0.5 N is acting.
Q5.
A spaceship of mass 9000 kg fires its engines and produces a thrust of 1800 N.
Calculate the acceleration of the spaceship. You do not need to give the unit.
Correct Answer: 0.20, 0.2, 0.200, 0.2000
0.20, 0.2, 0.200, 0.2000
Q6.
A train of mass 75 000 kg travels along horizontal track. The driving force is 40 000 N forwards, the frictional force is 4000 N and the drag force 6000 N. Calculate the acceleration of the train.
0.13 m/s$$^2$$
Correct answer: 0.40 m/s$$^2$$
0.40 m/s$$^2$$
0.54 m/s$$^2$$
0.67 m/s$$^2$$
2.5 m/s$$^2$$