P5 - Forces

Question 1

Scalar and Vector Quantities

Answer 1

Scalar quantities only have a magnitude
e.g. speed, distance
Vector quantities have both magnitude and direction
e.g. velocity, displacement

Question 2

What is a Force?

Answer 2

A push or pull on an object; they’re measured in Newtons (N)

Question 3

Contact and Non-Contact Forces

Answer 3

A contact force is when two objects have to touch to interact
e.g. tension, friction, air resistance, thrust, lift, reaction force
A non-contact force is when two objects don’t have to touch to interact
e.g. magnetic force, electrostatic force, gravity

Question 4

Newton’s Third Law

Answer 4

Whenever two objects interact, the forces they exert on each other are equal and opposite
- they are called an interaction pair, made of action and reaction forces

Question 5

Speed

Answer 5

Speed (m/s) = distance (m) ÷ time (s)
Average Speed (m/s) = total distance (m) ÷ total time (s)
Instantaneous Speed = speed at the moment in question

Question 6

Weight

Answer 6

Weight = how strongly gravity pulls on matter
Weight (N) = mass (kg) x gravitational field strength (N/kg)

Question 7

Acceleration

Answer 7

Acceleration (m/s2) = change in velocity (m/s) ÷ time (s)
Final velocity2 (m/s) - initial velocity2 (m/s) = 2 x acceleration (m/s2) x displacement (m)

Question 8

Newton’s Second Law

Answer 8

The acceleration of an object is proportional to the resultant force on an object. It is also inversely proportional to the mass of the object.
Force (N) = mass (kg) x acceleration (m/s2)

Question 9

Newton’s First Law

Answer 9

An object will continue at motion until a force is applied to it
Inertia = the amount/measure of how hard it is to change the motion of an object
Inertial mass (kg) = force (N) ÷ acceleration (m/s2)

Question 10

Centre of Mass/Gravity

Answer 10

The point where all weight can be considered to act from

Question 11

Finding the Centre of Mass/Gravity (Regular Objects)

Answer 11

1) draw two lines of symmetry
2) where these lines intercept is the centre of mass

Question 12

Finding the Centre of Mass/Gravity (Irregular Objects)

Answer 12

1) place a cork with a pin into a retort stand
2) create two points of suspension in the object
3) hang it up by the first point of suspension and place the plumb line in front of it
4) mark two point along this line and then join them together
5) repeat this with the second point of suspension
6) where the two lines intercept is the centre of mass/gravity