Newtons Laws Learning Intention To learn Newtons laws

Newton’s Laws

Learning Intention: To learn Newton’s laws, as well as recapping friction. Success Criteria: Newton’s laws will be used to solve problems, including looking at how much force it takes for a spacecraft to take-off.

Friction is a force which opposes motion. Cars slow down due to frictional forces between the tyres and the road surface, or when the driver applies the brakes which causes a frictional force to be applied to the brake disc.

Friction Click the image above for a video on car brakes.

Activity The class should be split into four groups, each given a large show-me-board. Each group has to answer one of these: i) Situations where friction is a good thing. ii) Situations where friction is a bad thing. iii) Ways of increasing friction. iv) Ways of reducing friction.

Newton’s st 1 Law An object will remain at rest or move at constant speed in a straight line unless acted on by an unbalanced force. 10 N Equal forces acting in opposite directions on an object are called balanced forces and are equivalent to no force at all.

Newton’s nd 2 Law When an object is acted on by a constant unbalanced force, the body moves with constant acceleration in the direction of the unbalanced force. Fun = ma Unbalanced Force (N) Acceleration (ms-2) Mass (kg)

EXPERIMENT 1 i) Set up the apparatus as shown below: QED Computer Light Gate Double card vehicle Pulley and thread Air Track Masses ii) Calculate the weight of the hanging mass (the applied force) and enter into the table in your workbook.

EXPERIMENT 1 iii) As the mass must be kept constant, any masses not on the hook must be attached to the vehicle. iv) Release the vehicle and read the value for acceleration from the computer. Record in your workbook. iv) Repeat for other applied forces (change the hanging mass). v) Plot a graph of force against acceleration. vi) State the relationship between Force and acceleration in your workbook.

The graph is a straight line passing through the origin, therefore force and acceleration are directly proportional.

Examples Now, work through this example as a class, completing the solution in your workbook: Example 1: An unbalanced force of 75 N acts on a mass of 15 kg. Calculate the acceleration of the mass. Example 2: Calculate the acceleration of the object below: 3 N 3 kg 15 N Example 3: Calculate the frictional force: a = 3 m/s 2 FF 12 kg 60 N

Examples Now, work through this example as a class, completing the solution in your workbook: Example 4: Calculate the engine force for this rocket to take off from Earth with an acceleration of 4. 8 ms-2. Assume frictional forces are negligible. Now, solve the examples from your workbook in your classwork jotter showing full working for each one.

Newton’s rd 3 Law Every action force has an equal and opposite reaction force. The two forces are sometimes called a ‘Newton Pair’. (e. g. Pushing a drawing pin, kicking a football, etc. )

Newton’s rd 3 Law A car is an example of a Newton Pair. The tyres push back on the road. The road pushes forwards on the tyres. (That’s why the car moves forward!!)

Newton’s 3 rd Law A rocket is pushed forward because the ‘propellant’ is pushed back. Propellant gases push rocket forwards making it accelerate Rocket motors push propellant gases backwards

EXPERIMENT 2 Your challenge is to demonstrate Newton’s third law by causing a straw to take part in a race across the room. You are only allowed to use a straw, string, balloons and sellotape.

NEWTON’S LAWS N 1: An object will remain at rest or travelling at a constant velocity unless acted upon by an unbalanced force. N 2: Fun = ma Unbalanced Force (N) Acceleration (ms-2) Mass (kg) For forces questions, draw a diagram showing ALL of the forces acting on an object. e. g. Parachutist e. g. Rocket taking off Rocket Thrust Air Resistance Mass Weight Air Resistance Weight

NEWTON’S LAWS N 3 – Every action has an equal and opposite reaction. A ‘Newton pair’ describes the action and reaction force: e. g. Action; Rocket ship pushes against propellant gases. Reaction; Propellant gases push against rocket ship. The Newton: the Newton is defined as the force required to accelerate a 1 kg mass at 1 ms-2. Friction: defined as a force that opposes motion.

KNOWLEDGE OF PHYSICS QUESTION 1 You have five minutes to answer the following question in your workbook. The answer will be assessed by your peers.

KNOWLEDGE OF PHYSICS QUESTION 2 You have five minutes to answer the following question in your workbook. The answer will be assessed by your teacher. The picture shows a dog team about to pull a sled through the snow. The human driving the sled states that Newton’s laws help to explain its motion. Use your knowledge of physics to expand on his statement.

Success Criteria: Newton’s laws will be used to solve problems, including looking at how much force it takes for a spacecraft to take-off. Tick off the box in your workbook when you have met the success criteria.

Now, use the space in your workbook to produce a summary of Newton’s laws. You may wish to produce concise bullet points, or draw a mind-map, or use any other useful revision technique. TEACHER CHECKPOINT : You should then give your workbook to your teacher for feedback.