P2.1 forces and their effects

P2.1 Forces and their effect

2.1.1 Resultant forces

2.1.2 Forces and motion

Forces can cause changes to the shape or motion of an object. Objects can move in a straight line at a constant speed. They can also change their speed and / or direction (accelerate or decelerate). Graphs can help us to describe the movement of an object. These may be distance–time graphs or velocity–time graphs.

You should be able to:

■ interpret data from tables and graphs relating to speed, velocity and acceleration

■ evaluate the effects of alcohol and drugs on stopping distances

■ evaluate how the shape and power of a vehicle can be altered to increase the vehicle’s top speed

■ draw and interpret velocity–time graphs for objects that reach terminal velocity, including a consideration of the forces acting on the object

Key words ForceMotionResultantStationaryVelocityAccelerationMassGradientSpeedStopping distanceReaction time

FrictionKinetic energyTerminal velocityElasticPotential energyWorkPowerMomentumConservation of momentum

If something is moving there is a force acting on it

To move something we need a force

A force is needed to change the shape of something

A force is a type of energy

Weight is a force

Mass is a force

Stretching a spring needs a force

A frictionless car does not need a force to keep it moving

Gravity is a type of force

Friction is a type of force

Forces always occur in pairs

P2.1.1 Resultant forcesa) Whenever two objects interact, the forces they exert on each other are equal and opposite.

b) A number of forces acting at a point may be replaced by a single force that has the same effect on the motion as the original forces all acting together. This single force is called the resultant force.

c) A resultant force acting on an object may cause a change in its state of rest or motion.

d) If the resultant force acting on a stationary object is:

■ zero, the object will remain stationary

■ not zero, the object will accelerate in the direction of the resultant force.

𝑎=𝐹𝑚

P2.1.2 Forces and motiona) The acceleration of an object is determined by the resultant force acting on the object and the mass of the object.F = m × a

b) The gradient of a distance–time graph represents speed.

c) Calculation of the speed of an object from the gradient of a distance–time graph.

d) The velocity of an object is its speed in a given direction.

e) The acceleration of an object is given by the equation:

𝑎=𝑣−𝑢𝑡

f) The gradient of a velocity–time graph represents acceleration.

g) Calculation of the acceleration of an object from the gradient of a velocity–time graph.

h) Calculation of the distance travelled by an object from a velocity–time graph.

Travel graphs

Is Dolly a clone of sheep A or B?

Explain your answer.

Dolly is a clone of sheep ........................

reason why