P8: Forces in Balance

Question 1

What is displacement?

Answer 1

Distance without a change in direction.

Question 2

What is a vector quantity? What are some examples?

Answer 2

Physical quantities with both size/magnitude and direction.
E.g. Velocity, displacement, acceleration, momentum, gravitational field strength, weight.

Question 3

What are scalar quantities? What are some examples?

Answer 3

Physical quantities with size/magnitude but no direction.
E.g. Speed, time, mass, distance, energy, power.

Question 4

What are forces?

Answer 4

A push or pull that acts on an object because of its interaction with another object. Can change shape of an object or change its state of rest or motion.

Question 5

What are contact/non-contact forces?

Answer 5

Contact forces are when 2 objects must touch to interact.
Contact - Friction, Air resistance, Tension, Thrust
Non contact - Magnetic, Electrostatic, Gravity

Question 6

What is Newton’s 3rd Law of Motion?

Answer 6

When two objects interact with each other, they exert equal and opposite forces.

Question 7

What is friction?

Answer 7

Force exerted by a surface against an object when it moves across it.

Question 8

What is the resultant force?

Answer 8

The overall force of an object as a result of all forces acting on the object being combined.

Question 9

What is Newton’s 1st Law of Motion?

Answer 9

If the forces acting on an object are balanced and the resultant force is zero, the object will either remain stationary or move at a constant velocity.

Question 10

What is the moment of a force and how can it be increased?

Answer 10

• The moment of a force is a measure of the turning effect of a force on an object.
• Can be increased by increasing the size of the force, using a spanner with a longer handle.

Question 11

What do levers do?

Answer 11

Levers can be used to exert a force greater than the effort to make object turn more easily - force multiplier.

Question 12

What is the equation for the moment of a force?

Answer 12

Moment (Nm) = Force x Perpendicular Distance

Question 13

What are gears?

Answer 13

Gears are used to change the moment of a turning effect by changing speed, force or direction by rotation.

Question 14

What do low/high gears do?

Answer 14

Low gear gives low speed but high turning effect - Small gear wheel drives a large one.
High gear gives high speed but low turning effect - Large gear wheel drives a small one.
Second gear turns in opposite direction.

Question 15

What is the centre of mass of an object?

Answer 15

The point at which its mass it thought of as being concentrated - point at which weight of an object acts.
For regular object it is where lines of symmetry meet.

Question 16

How can you find the centre of mass of an irregular object?

Answer 16

Put hole in the corner of a card and suspend from a rod. Use plumb line to draw vertical line on card from rod. Repeat using different corner. Point that lines meet is the centre of mass.