Forces

What do scalar quantities have?

Magnitude only

What do vector quantities have

Both magnitude and direction

Define force

A force is a push or pull that acts on an object due to the interaction with another object

Name 4 contact forces

• Friction

• Air resistance

• Tension

• Normal contact force

Name 3 non-contact forces

• Weight

• Gravitational force

• Electrostatic force

• Magnetic force

Define weight

The force acting on an object due to gravity

Where is the weight of an object?

A single point called the centre of mass

What is the relationship between a weight of an object and mass?

Directly proportional

Define work done (2)

Energy transferred from one store to another

OR

When a force causes an object to move

Define resultant force

The total force acting on an object

How can an object's shape change?

• Stretching

• Bending

• Compressing

What is a change in shape called?

Deformation

explain why, to change the shape of an object , more than one force has to be applied

A single force would only make an object move in the direction in which the force is applied

What is the difference between elastic and inelastic deformation?

Elastic deformation is reversible so an object will return to its original shape However, inelastic deformation is not, leading to permanent changes in the shape of the object

What is the relationship between the extension of an elastic object and the force applied?

Directly proportional unless the limit of proportionality is exceeded

what is meant by the elastic limit/limit of proportionality of a material?

The furthest point a material can be stretched or deformed while being able to return to its previous shape

Describe the difference between a linear and non-linear relationship between force and extension

Linear

• The gradient of the force-extension graph is = spring constant

  ↳ Force and extension are directly proportional

Non-Linear

• Opposite

  ↳ Extension increases more for each unit increase in force

Describe the energy transfer involved when a force stretches or compresses a spring

• Force does work on the spring

• And energy is transferred mechanically to the elastic potential energy store of the object

• Only if the spring is not inelasticaly deformed

• Work done=elastic potential energy stored

Define moment

The turning effect of a force

What is the moment of a balanced object?

Clockwise moment = anti-clockwise moment about that pivot

What are the components of a lever?

• Pivot → Turning point

• Effort → The force used to move a load over a distance

• Load → The overall force which is being exerted

What are gears?

wheels with toothed edges that rotate on an axle or shaft

How does a gear transmit the rotational effect of a force?

• The teeth of one gear fits

• When the motor of one gear is turned on, this creates a moment

• The moment is passed down via the interlocking teeth

• The direction of the gears alternate

What effects the moment?

Larger moment → distance from the center is larger

What is the relationship between pressure and depth?

Directly proportional → as depth increases, pressure also increases

Explain why, in a liquid, pressure at a point increases with the height of the column of liquid above that point

• The depth is increased

  ↳ Number of particles above the point increases

• So the weight of the liquid above increases

• Which increases the pressure

Explain why, in a liquid, pressure at a point increases with the density of the liquid

• Denser liquid

  ↳ More particles in a certain space

• More particles can collide

• Which increases pressure

Define upthrust

The resultant force upwards when a partially/totally submerged object experiences pressure

What causes an object to sink?

When upthrust is less than the weight of the object

What causes to float?

When upthrust is larger than the weight of an object

Define atmosphere

A thin layer of air around the Earth

Explain why atmospheric pressure decreases with increasng altitude

• As altitude increases, the number of air molecules decreases

• So the weight of air decreases

• Because there is less air above a surface

What creates atmospheric pressure?

Air molecules colliding with a surface which creates a force

What are the typical speeds for a person walking, running, and cycling?

• Walking: 1.5m/s

• Running: 3m/s IT DOUBLES

• Cycling: 6m/s

How do you find the speed of an object on a distance-time graph?

Find the gradient of the line

What does each section of the graph tell you?

A) Increasing speed

B) Constant speed

C) Decreasing speed

D) Stationary

What does each section of the graph tell you?

A) Accelerating

B) Constant speed

D) Decelerating

D) Stationary (Back to the start)

How can the displacement of an object be calculated?

The area under the velocity-time graph

Define terminal velocity

The maximum speed of an object

How is terminal velocity reached?

When the forces moving an object are balanced by its frictional forces

Define fluid

A substance that can flow → Liquid and gas

What happens when an object falls?

• Initially accelerates downwards due to gravity

• As speed increases, air resistance/drag is also increased

• The object eventually reaches terminal velocity when the resultant force is 0

State Newton's first law

If the resultant force of an object is 0 and:

• Stationary → the object remains stationary

• Moving → the object continues to move at the same time and in the same direction

Define inertia

The tendency of objects to continue in their state of rest or uniform motion

State Newton's second law

F=ma

The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object

Define inertial mass

The ratio of force over acceleration

What does inertial mass measure?

How difficult it is to change the velocity of an object

State Newton's third law

When two objects interact, they exert a force on eachother which are equal and opposite in direction

How do you calculate stopping distance?

Thinking distance + braking distance

How does a car slow down?

• A force is applied onto the brakes

  ↳ work is done by friction between the brakes and the wheel

• Reduction in kinetic energy

  ↳ slows down and increases the temperature of the brakes

what are the dangers of braking too fast?

• Greater the braking force, the greater the deceleration of the vehicle

• Large decelerations could cause the brakes to overheat

• Which would cause a loss of control

What is the conservation of momentum?

The total momentum before an event is = to the total momentum after an event in a closed system