Contact and Non-Contact Forces -
• A force is a push or pull, that acts on an object, due to its interaction with another
object. Measured in newtons (N). For example when a hand pushes it box (5N).
• The force is the magnitude. Forces also have direction, e.g. to the right.
• This means forces are classed as ‘Vector quantities’ as they have both magnitude and
direction.
• Contact forces are when two objects are physically touching. For example: friction
between a skateboard and pavement, air resistance (collision between object and air
particles), tension (pulling force through rope).
• The ‘normal contact force’ is the ‘reaction force’. As a rock on a table has mass, it
exerts a force downwards (weight). However, the table must be exerting an equal and
opposite upwards force to keep it there.
• Non-contact don’t require them to be touching. They can act through empty space.
Types: gravitational, magnetic and electrostatic. They are ‘fields of influence’ as the
force can act on anything in the surrounding area. For example gravity is a force of
attraction between any two objects that have mass, even if not touching.
• Magnetic can be attractive or repulsive depending on the poles. Electrostatic are the
same.
• The strength of the force decreases as the object gets further apart.
Scalar and Vector Quantities -
• Scalars are physical quantities that only have a magnitude (size, measured with a
number) but no direction.
• For example, if a car has a speed of 22/ms, this is the magnitude. This by itself doesn’t
have a direction so is scalar.
• Other examples include distance, mass, temperature, time, power.
• Vectors have both a magnitude and a direction. This includes velocity, displacement,
acceleration, force and momentum. It has the direction. For example, 4km north.
• We represent these with arrows. The length of it represents the magnitude. The way
it’s pointing shows direction.
• We can show this through negative vectors. 2km west = -2km east (backwards).
• Displacement is the movement from one specific point. So if they move 200m right but
100m left after, the displacement is 100m right.
Free Body and Resultant Diagrams -
• Free body diagrams show all the forces acting on an object. This is done through force
arrows. For example, a plane has thrust (forward), air resistance (backwards), lift
(upwards) and weight (downwards).
,• All forces are vectors so must have a magnitude and direction. Direction shows which
way the arrows are pointing. The length shows the magnitude (can be labelled, e.g.
80,000N).
• Some forces will cancel each other out. What we have left is the resultant force
(overall force on an object). Do right – left or up – down, or describe the direction. This
can affect speed and direction.
• If there is no resultant force the object is in ‘equilibrium’.
Resolving Vector and Scale Diagrams -
• We can represent the free body resulting force on a scale drawing/diagram. 1cm is 1
newton. Place them tip to tail. Draw a line from the starting point to the end point.
Measure it with a ruler. You can also use Pythagoras for this.
• To measure the direction of the force, measure the angle with a protractor from the
north point. So the result would be e.g. 5N at a bearing 37N from north.
• In a drawing with three separate arrows, just arrange them tip to toe again. If they all
join up perfectly there must be zero resultant force.
• We can resolve vectors by splitting it up into its horizontal and vertical components.
Elasticity, Spring Constant and Hooke’s Law -
• A force can cause an object to compress, stretch or bend. This can apply to balls or
even phones, however these are less elastic so it is harder to notice change of shape.
• We need to apply more than one force for these (e.g. pushing upwards would just
make it move, not compress).
• When an object changes shape we say it is ‘deformed’. Deformation types:
- Elastic: An object returns back to its original shape after the force is removed.
- Inelastic: Doesn’t return to normal shape, stays deformed. ‘Plastic deformation’.
• Extension is the increase in length of a spring when it’s stretched. If we hang it from a
solid support, we can measure how the length changes as we add downwards force.
The spring’s own mass exerts a force downwards (weight). The natural length will be
shorter than this, however this tends to be small so we ignore this.
• Extension can also refer to a decrease in length if the spring is compressed.
• If we add a mass, this extends the length – the extension. The solid support (e.g. a
table) will be exerting an equal but opposite force upwards. As we add more mass, the
extension increases proportionally. F x E. Directly proportional.
• How much it extends is represented by its spring constant (k). So f = ke. k in N/m, this
is the spring constant. This shows how many newtons it takes to stretch the object by
1m. The higher the constant, the stiffer the material.
, • We can plot this on a graph of force (y) and extension (x). Because it’s a straight line
that passes through the origin, we know they’re directly proportional. This is known as
‘Hooke’s Law’. This is elastic deformation.
• At some point this line will start to curve. This is known as the ‘elastic limit’ or ‘limit of
proportionality’. At this point Hooke’s law no longer applies and it may become
inelastically deformed.
Elastic Potential Energy -
• F = ke OR Force (N) = spring constant (N/m) x extension (m). A lower spring constant
means it’s more elastic and easier to stretch.
• Ee = 1/2ke^2. Elastic potential energy (J) = ½ x spring constant (N/m) x extension^2
(m).
- This is the energy transferred to an object as it’s stretched. 100J used to stretch a
spring would be transferred to its elastic potential energy store. When you let it go, this
is transferred back out to a different form such as kinetic energy.
• We can find the extension by subtracting the new length from the original length. To
find spring constant do force/extension. We can then plug this into the Ee equation.
• In a force, extension graph the gradient of the line is the spring constant (before elastic
limit). The area under the line is equal to the energy transferred to the spring.
Moments -
• A moment is the rotational or turning effect of a force. For example, apply a force to a
spanner just turns it rounds a central point (a pivot). This turning effect is the moment.
• We use M = Fd. Moment (nm) = force (N) x distance (m).
• The distance is the perpendicular distance between the pivot and the place where the
force is applied. Highest moment is a larger force furthest away from the force.
• If we applied the force at a weird angle, the perpendicular distance would be much
smaller, resulting in a smaller moment.
• We can rearrange our equation to get the required force or distance.
• You can have more than one moment acting on the same object. In a seesaw, the
pivot is the middle. To work out the overall moment (total clockwise – total
anti-clockwise)
• We talk about moments in terms of clockwise or anti-clockwise.
Moments Continued -
• Levers transmit the turning effect of a force. We apply an input force and this creates
an output force somewhere else. If the input and output are in different sides, they act in
different directions (e.g in scissors). If they’re on the same side, they act in the same
direction (e.g. wheelbarrow, input up, output up).
• A force is a push or pull, that acts on an object, due to its interaction with another
object. Measured in newtons (N). For example when a hand pushes it box (5N).
• The force is the magnitude. Forces also have direction, e.g. to the right.
• This means forces are classed as ‘Vector quantities’ as they have both magnitude and
direction.
• Contact forces are when two objects are physically touching. For example: friction
between a skateboard and pavement, air resistance (collision between object and air
particles), tension (pulling force through rope).
• The ‘normal contact force’ is the ‘reaction force’. As a rock on a table has mass, it
exerts a force downwards (weight). However, the table must be exerting an equal and
opposite upwards force to keep it there.
• Non-contact don’t require them to be touching. They can act through empty space.
Types: gravitational, magnetic and electrostatic. They are ‘fields of influence’ as the
force can act on anything in the surrounding area. For example gravity is a force of
attraction between any two objects that have mass, even if not touching.
• Magnetic can be attractive or repulsive depending on the poles. Electrostatic are the
same.
• The strength of the force decreases as the object gets further apart.
Scalar and Vector Quantities -
• Scalars are physical quantities that only have a magnitude (size, measured with a
number) but no direction.
• For example, if a car has a speed of 22/ms, this is the magnitude. This by itself doesn’t
have a direction so is scalar.
• Other examples include distance, mass, temperature, time, power.
• Vectors have both a magnitude and a direction. This includes velocity, displacement,
acceleration, force and momentum. It has the direction. For example, 4km north.
• We represent these with arrows. The length of it represents the magnitude. The way
it’s pointing shows direction.
• We can show this through negative vectors. 2km west = -2km east (backwards).
• Displacement is the movement from one specific point. So if they move 200m right but
100m left after, the displacement is 100m right.
Free Body and Resultant Diagrams -
• Free body diagrams show all the forces acting on an object. This is done through force
arrows. For example, a plane has thrust (forward), air resistance (backwards), lift
(upwards) and weight (downwards).
,• All forces are vectors so must have a magnitude and direction. Direction shows which
way the arrows are pointing. The length shows the magnitude (can be labelled, e.g.
80,000N).
• Some forces will cancel each other out. What we have left is the resultant force
(overall force on an object). Do right – left or up – down, or describe the direction. This
can affect speed and direction.
• If there is no resultant force the object is in ‘equilibrium’.
Resolving Vector and Scale Diagrams -
• We can represent the free body resulting force on a scale drawing/diagram. 1cm is 1
newton. Place them tip to tail. Draw a line from the starting point to the end point.
Measure it with a ruler. You can also use Pythagoras for this.
• To measure the direction of the force, measure the angle with a protractor from the
north point. So the result would be e.g. 5N at a bearing 37N from north.
• In a drawing with three separate arrows, just arrange them tip to toe again. If they all
join up perfectly there must be zero resultant force.
• We can resolve vectors by splitting it up into its horizontal and vertical components.
Elasticity, Spring Constant and Hooke’s Law -
• A force can cause an object to compress, stretch or bend. This can apply to balls or
even phones, however these are less elastic so it is harder to notice change of shape.
• We need to apply more than one force for these (e.g. pushing upwards would just
make it move, not compress).
• When an object changes shape we say it is ‘deformed’. Deformation types:
- Elastic: An object returns back to its original shape after the force is removed.
- Inelastic: Doesn’t return to normal shape, stays deformed. ‘Plastic deformation’.
• Extension is the increase in length of a spring when it’s stretched. If we hang it from a
solid support, we can measure how the length changes as we add downwards force.
The spring’s own mass exerts a force downwards (weight). The natural length will be
shorter than this, however this tends to be small so we ignore this.
• Extension can also refer to a decrease in length if the spring is compressed.
• If we add a mass, this extends the length – the extension. The solid support (e.g. a
table) will be exerting an equal but opposite force upwards. As we add more mass, the
extension increases proportionally. F x E. Directly proportional.
• How much it extends is represented by its spring constant (k). So f = ke. k in N/m, this
is the spring constant. This shows how many newtons it takes to stretch the object by
1m. The higher the constant, the stiffer the material.
, • We can plot this on a graph of force (y) and extension (x). Because it’s a straight line
that passes through the origin, we know they’re directly proportional. This is known as
‘Hooke’s Law’. This is elastic deformation.
• At some point this line will start to curve. This is known as the ‘elastic limit’ or ‘limit of
proportionality’. At this point Hooke’s law no longer applies and it may become
inelastically deformed.
Elastic Potential Energy -
• F = ke OR Force (N) = spring constant (N/m) x extension (m). A lower spring constant
means it’s more elastic and easier to stretch.
• Ee = 1/2ke^2. Elastic potential energy (J) = ½ x spring constant (N/m) x extension^2
(m).
- This is the energy transferred to an object as it’s stretched. 100J used to stretch a
spring would be transferred to its elastic potential energy store. When you let it go, this
is transferred back out to a different form such as kinetic energy.
• We can find the extension by subtracting the new length from the original length. To
find spring constant do force/extension. We can then plug this into the Ee equation.
• In a force, extension graph the gradient of the line is the spring constant (before elastic
limit). The area under the line is equal to the energy transferred to the spring.
Moments -
• A moment is the rotational or turning effect of a force. For example, apply a force to a
spanner just turns it rounds a central point (a pivot). This turning effect is the moment.
• We use M = Fd. Moment (nm) = force (N) x distance (m).
• The distance is the perpendicular distance between the pivot and the place where the
force is applied. Highest moment is a larger force furthest away from the force.
• If we applied the force at a weird angle, the perpendicular distance would be much
smaller, resulting in a smaller moment.
• We can rearrange our equation to get the required force or distance.
• You can have more than one moment acting on the same object. In a seesaw, the
pivot is the middle. To work out the overall moment (total clockwise – total
anti-clockwise)
• We talk about moments in terms of clockwise or anti-clockwise.
Moments Continued -
• Levers transmit the turning effect of a force. We apply an input force and this creates
an output force somewhere else. If the input and output are in different sides, they act in
different directions (e.g in scissors). If they’re on the same side, they act in the same
direction (e.g. wheelbarrow, input up, output up).
