P8

Question 1

Contact forces

Answer 1

• friction
• air resistance
• water resistance
• tension
• compression forces
• normal contact forces (objects interacting)

Question 2

Non contact forces

Answer 2

• magnetic
• electrostatic
• gravitational
• weight force

Question 3

Where do force arrows go from?

Answer 3

The centre of mass

Question 4

Newton’s Third Law

Answer 4

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

Question 5

Newton’s First Law of Motion

Answer 5

If the forces acting on an object are balanced, the resultant force is zero, the object will either:
• be at rest/stationary
• object will move at a constant speed and in the same direction

Question 6

Newton’s Second Law

Answer 6

mass x acceleration = force
F = ma
No net force = no acceleration/change in speed

Question 7

What is the centre of mass?

Answer 7

• point of an object at which all the mass of an object is concentrated

Question 8

Finding the centre of mass of a regular/symmetrical shape:

Answer 8

• draw dotted lines from each point of the shape
• where the lines cross = centre of mass

Question 9

How to find the centre of mass of an irregular shape

Answer 9

• suspend the shape from a hole near the edge
• tie a plumbline to the pivot point
• let the shape come to equilibrium
• trace a line across the plumbline
• repeat with two more holes
• centre of mass is where the lines cross

Question 10

Parallelogram of Forces - Compass Method

(Longer method)

Answer 10

• choose a scale
• draw one of the forces to scale
•draw the second force, with the correct angle in between.
• adjust your compass to the length of a force.
• place the compass on the end of the force and sketch a curve.
• do the same from the other point.
• draw two lines from the tips of the arrows to the cross.
• draw a diagonal vector from the origin point.
• measure this for the resultant force