Topic 8 - Forces in Balance

Question 1

What is displacement?

Answer 1

Distance travelled without a change in direction.

Question 2

What are vectors?

Answer 2

Physical quantities which have direction.

Question 3

What are three examples of vectors?

Answer 3

Acceleration, weight, gravitational field strength.

Question 4

What are scalars?

Answer 4

Physical quantities with no specific direction.

Question 5

What are three examples of scalars?

Answer 5

Mass, distance, time.

Question 6

What is magnitude?

Answer 6

The size of a quantity.

Question 7

How do you show the size of a vector?

Answer 7

1) The direction of the arrow shows the direction of the vector.
2) The length of the arrow represents its magnitude.

Question 8

What is Newton’s third law?

Answer 8

That all objects have an equal and opposite force when interacting.

Question 9

What is a driving force?

Answer 9

Force of a vehicle which makes it move.

Question 10

What is friction?

Answer 10

The force opposing motion between two objects.

Question 11

What is the resultant force?

Answer 11

The force that is equal to the sum of all forces acting on it.

Question 12

What is Newton’s first law?

Answer 12

If an object has 0 force applied on it it will remain stationary or move in the same direction at the same speed if it was already moving.

Question 13

What two factors influence the size of a moment?

Answer 13

Increasing the size of a force and increasing the perpendicular distance to the pivot.

Question 14

What is the name for the weight of an object?

Answer 14

The load.

Question 15

What is the force someone applies in a momentary sense called?

Answer 15

The effort.

Question 16

What is the equation for a moment?

Answer 16

Moment (M) (Nm) = Force (F) (N) x perpendicular distance (d) (m)

Question 17

What is a force multiplier?

Answer 17

A lever used to multiply momentary force.

Question 18

What is a free body force diagram?

Answer 18

A diagram showing the forces acting on an object without representing other forces.

Question 19

What is the parallelogram of forces?

Answer 19

A geometrical method used to find the resultant force of two forces which do not sit on the same line of action.

Question 20

What is the principle of moments?

Answer 20

For an object in equilibrium, the sum of clockwise moments = the sum of anti-clockwise moments.

Question 21

What is the difference between a vector and scalar quantity?

Answer 21

A vector quantity has magnitude and direction

A scalar quantity has magnitude only

Question 22

How do you draw a Scale diagram?

Answer 22

Choose a scale e.g. 1N to 1cm.

Draw the lengths in this scale.

Question 23

What do forces do to an object?

Answer 23

They can change shape of an object or its state of rest or motion.

Question 24

What are some examples of Newton’s third law?

Answer 24

A boxer who punches a bag receives an equal and opposite force from the bag.

The weight of an objecct is the force of gravity on the object due to the Earth. The object exerts an equal and opposite force on the Earth.

When two people pull a rope from each side they move towards each other as they exert a force on each other.

Question 25

What happens when a car moves forward (in terms of forces)?

Answer 25

The force of the friction of the road on the tyre is in the forward direction. The force of friction on the road is in the reverse direction. These forces are equal and opposite to each other.

Question 26

What is resultant force equal to?

Answer 26

The differences of the two forces acting on an object. It is measured in the direction of the larger force.

Question 27

How can you increase the moment of a force?

Answer 27

Increase the size of the force. Use a spanner with a longer handle to increase perpendicular distance.

Question 28

What is the weight of an object called?

Answer 28

The load.

Question 29

What is the force applied on an object called?

Answer 29

The effort.

Question 30

What is moment of a force equal to?

Answer 30

Moment = force x perpendicular distance

Question 31

A force of 50N is exerted on a hammer length 0.5. Calculate the moment of the force?

Answer 31

50 x 0.5 = 25Nm

Question 32

What do gears do?

Answer 32

Multiply the effect of a turning force.

Question 33

What happens when in low gear on gear wheels?

Answer 33

A small gear wheel driven by the engine shaft is used to turn a large gear wheel. So the output shaft turns slower than the engine shaft. The turning effect of the output shaft is greater than the turning effect of the engine shaft. Low gear gives low speed and a high turning effect.

Question 34

What happens when a high gear is chosen?

Answer 34

A large gear wheel driven by the engine shaft is used to turn a small gear wheel on the output shaft. The output shaft turns faster than the engine shaft. The force of the smaller gear wheel acts nearer to its shaft than the force of the larger gear wheel acting on its shaft. High gear gives high speed and a low turning effect.

Question 35

What is the centre of mass of an object?

Answer 35

The point where its which mass can be thought of as being concentrated.

Question 36

How do you use symmetry to find centre of mass?

Answer 36

If the object has more than one axis of symmetry, the centre of mass is where the axes meet.

Question 37

On a level seesaw, what is true about moments?

Answer 37

The anticlockwise and clockwise moments are equal.

Question 38

How do investigate the parallelogram of forces?

Answer 38

Draw the angles between values of force to make a parallelogram. The perpendicular bisector represents the vertical line through the point where the three strings meet. Adjacent sides of the parallelogram at angles to the vertical line represent tensions in a string. The line bisecting the two forces is the resultant force.

Question 39

When is an object at equilibrium?

Answer 39

The resultant force on the object is zero. The forces acting on the object have no overall turning effect.

Question 40

How do you find if an object is in equilibrium?

Answer 40

The lines of action of the forces are parallel, the sum of the forces in one direction must be equal to the sum of the forces in the opposite direction. This means that the resultant force on the object is zero. If the lines of action of the forces are not all parallel, the forces can be resolved into two components along the same perpendicular lines. The components along each line must balance out if the resultant force is zero and it is at equilibrium.