Newton's second law relates the resultant force acting on a body and its acceleration:
\(F=ma\)
Because acceleration is defined as the rate of change in velocity, Newton's second law can also be expressed as the rate of change of a momentum of a body is proportional to the resultant force and is in the same direction as the force.
\(F={\Delta (mv)\over t}\)
Key Concepts
Since \(F={\Delta (mv) \over t} \Rightarrow \Delta(mv)=Ft\). Therefore, change in momentum (impulse) can be found from the area under a force - time graph.
This experimental set-up can be used to verify Newton's second law.
There are two free bodies to consider separately in this question:
- \((\downarrow)\) The hanging mass falls because its weight is larger than the tension
- \((\rightarrow)\) The mass on the table accelerates because the tension is larger than friction
Applying Newtons law to both blocks gives an equation for the acceleration.
Use quizzes to practise application of theory.
START QUIZ!
Fill in the gaps in this statement of Newton's second law
acceleration, mass, momentum, direction, inversely, unbalanced
The of a body is directly proportional to the force acting on it and proportional to it's .
or/
The rate of change of is directly proportional to the unbalanced force acting on the body and takes place in the same .
A mass of 2 kg is accelerated, at a constant rate, from rest to 2 ms-1 in 2 s.
The force acting on the body is
a = (2 - 0)/2
F = ma
A car travels up a steep hill in a straight line at 50 kmh-1 .
Which of the following statements are true?
Constant speed and constant direction means constant velocity so forces balanced.
A car travels around a corner at constant speed on a horizontal surface.
Which of the following statements are true?
The direction changes so velocity is not constant so forces not balanced.
In the vertical plane mg = N
Speed is constant so friction = air resistance in the forward direction but there is a component of friction perpendicular to the direction of travel.
The diagram shows the forces acting on a car
Which force is friction?
Friction between the wheels and ground pushes the car forward
The diagram shows the forces acting on a car
The forces are balanced so velocity is constant
The car is most probably travelling to the left but it could be going to the right if force B is something pulling the car and A is the front wheels braking
The diagram shows the forces acting on a car
What is the acceleration if A is increased to 1.5 kN?
a = F/m = 500/1000 negative since to the left
An unbalanced force of 100 N acts on a body for 5 seconds.
The change in momentum is:
F = Δmv/t so Δmv = F x t
The graph represents the force acting on a body.
The change in momentum is:
Change in momentum (impulse) = area
Alice is in the elevator
Alice definitely has :
Unbalanced force is up so acceleration is up. Could be moving down slowing down.
Water, travelling horizontally, hits a wall with a velocity of 5 ms-1 after hitting the wall the water the runs down it to the ground. If the water is flowing at a rate of 2 liters per second:
The mass of water hitting the wall per unit time = kgs-1
The rate of change of momentum = N
The force exerted by the wall onto the water = N
1 liter of water = 1 kg
rate ocf change of momentum = mass per unit time x change in velocity
The pink block accelerates to the right at 0.5 ms-2.
If the mass of the yellow block is 1 kg what is the tension in the string?
mg - T = ma = 0.5
10 - T = 0.5
How much of Newton's second law have you understood?
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